Monotheism - single-god religion - has done more harm to humanity than any other belief system. Violence, ignorance, sectarianism, intolerance, backwardness and confused morality are the biggest side-effect of dogmatic belief in God. To win, for humanity, we need to remove the sources of fundamentalism and bigotry that hold back entire cultures. If you argue well, presenting facts and taking emotions into account, we can win the war against the idea of god by reducing the firmness of belief in it. Any reduction in the power of organised monotheistic religions is a victory. If you argue with a theist long enough and well enough they may become agnostics, disillusioned with revelation yet still hold the belief that something divine exists. This is still a victory. How do you attain these victories? Because religion and god-belief is based on wishful thinking and delusion, the best weapon we have is the truth.
Historical Criticism: All religions evolved from previous religions and beliefs. A sure way to undermine belief is to point out all the elements of the religion that were copied from previous religions.
Comparative Religion: Most arguments they give for their religion will apply to many religions. If they believe in God, point out that it doesn't mean that any particular religion is true. If they believe in a historical Jesus, point out that everything written about him was by followers, and that followers of other religious leaders are known to have hugely exaggerated their successes and lives.
Schisms and Splits: All religions have split into factions and reasons often centre around the most illogical and least functional parts of the religion's doctrine. Knowing the history of the Arian/Pauline debates of Christianity shows us that a highly illogical and unstable part of Christian doctrine is that surrounding the relationship between Jesus and God. In Islam, the major divides of Sunni, Shia and Shi'ite have centered around the succession of power after Muhammad. These divides exist because important problems exist with the central theology and history of the religion. Don't let these issues fade!
Logic and Myth: Most religions contain stories, myths, explanations and fables that make almost no sense. Because they become part of culture they still get accepted. To explain 'sin' in terms of the choices of Adam and Eve is ridiculous, for example, but because the story is familiar, it gets trotted out unquestioned. Skeptical websites list the many contradictions and absurdities in the myths of world religions; when your deluded opponent alludes to these stories, research them and list a few of the nonsensical elements.
Moral Examples: The theist will almost certainly make claims that their religion causes moral behaviour. Don't forget though that atheists do good without the tempting reward of heaven, and avoid doing evil because it is wrong, not because they want to avoid hell. Whatever their arguments are, you need to point out that all religions claim that they represent better morals - and they all set the criteria so that when you measure success, the religion comes out best. Despite any theory, make sure you point out that the main monotheistic religions have the worst historical records!
Science and philosophy have often battled against religion. To debate religious topics, you must be well-versed in some or all of the following areas of science:
The Problem of Evil is a most-important area of theology and represents the biggest failure in the whole idea of a good god. I have a collection of pages on this problem on my Bane Of Monotheism website:
If God is all-powerful and all-good, it would have created a universe in the same way it created heaven: with free will for all, no suffering and no evil. But evil and suffering exist. Therefore God does not exist, is not all-powerful or is not benevolent (good)1. Such arguments have been used by many philosophers as evidence against belief in god2,3. A theodicy is an attempt to explain why a good god would have created evil and suffering. The most popular defence is that it is so Humans could have free will. However the entire universe and the natural world is filled with suffering, violence and destruction so any Humanity-centric explanation does not seem to work.”
There is much evidence that if there is a God, it is an evil god. See God Must Be Evil (If It Exists).
Most people do not belong to a religion because they have rationally chosen it after purveying the available evidence. Most people's justifications for their own religion are concocted after they self-identify. This is because most people fall into a religion socially or through parental pressure. It is only occasionally that a person sits down to examine the merits of competing religions, and most the time when they do this, it is because a new influence in their life is already changing them. Psychological, emotional and societal pressure is generally much more important than factual debate.
So to release a person from the intellectual shackles of religion, you generally need to approach them with the right demeanor, acting responsibly, calmly, confidently, but never being self-glorifying or sanctimonious. If they think you are worthless, a loser, biased, then they will not accept your arguments. If they start off thinking you are biased, as they probably will if you present yourself with different religious beliefs to them, then the way to overcome their judgement is to be a professional and polite in all conversation with them. Make them see you as considered and upstanding; you must gain respect.
If you present yourself, calmly, rationally, peacefully, in a friendly manner, then you can make a large amount of ground without even trying. Closely knit religious social groups often become deluded as to what atheists are like, for example in some parts of the Bible belt, or in some entire countries, atheists can be rare. Smash misconceptions by simply being nice.
There are too many dumb atheists who argue are arrogant and annoying and these only serve to solidify the theist's opinion that they are in the moral high ground and silently strengthen their commitment to their current position.
Fundamentalists have to be taken carefully, and slowly, and the best line of attack is to come over as friendly and acceptably as you can. In effect you have to get much deeper into them, you have to make a bigger (and unobtrusive) impression on them. They are very willing to jump on to a defensive rant, or to block you out, if you show signs of arguing offensively ("like all the others"). They love to find ways in which they can prove they are better than you in order to "prove" that their theology is equally untouchable.
Bad psychology will prevent your arguments from making an impact, and can turn a winning argument into a lose. Good psychology will turn a draw into a win and give you a good reputation as an arguer rather a reputation for being argumentative.
Develop your look and your appearance. Yes, we are using every trick in the book here! Dress smartly but no ties for crying out loud - that's what evangelists and mormons wear! Keep good eye contact, don't look at your feet as you talk. When they are wrong say, "Are you sure?". Even if you cannot prove something you can state, "Are you sure that's true?" and you allow them to think about the possibility that it isn't. Smile! Smile when they make a good point! Smile when they say something clever! Reward them for any intelligent comments, as it is through intelligence and good-thinking that they will eventually save themselves.
Do not constantly engage those around you in powerful argumentation. Have more skill than to approach everyone with a philosophical sledgehammer. In most areas in Europe religion is something that other people get up to. The average liberal European does not participate in his own religion. If we are stupid, and suddenly barrage them with theology we can have the reverse effect to what we intend. We can cause them to pay attention to their religion when previously they paid none. We should not force an issue when they are religiously placid and undefined, we can end up turning a neutral situation into a loss when the original situation was fine. Restraint!
If someone is living a fine life, mostly devoid of religion, and they themselves do not talk about religion, then there is little need to bother them. By assaulting them with questions about their little beliefs, you may turn them into bigger parts of their self-image.
Constantly engaging people in a demanding way causes a psychological arms war, where their responses are against your approach rather than your arguments. Be peaceful and considerate, yet clever. Commend them on their (attempted!) good arguments - make them feel good about their debate with you, even while you are dismantling their crazy ideas. Be civil!
Watch out for reverse psychology. If we broadcasted a news report saying how bad, uncouth and dangerous a music group is then we will almost definitely cause their sales to rise! Be careful that your criticisms work for the person you are talking to. There is no point deriding Christian ideas about female inferiority, if you happen to be talking to a person who agrees with that stance!
Be courteous in public. Do not spit upon Christians, cursing them as a group. This is known as prejudice, pure and simple. Challenge doctrine, and avoid personal insults. You will only make people gather around your victim and defend them (in their hearts or even in action). Remain focused on the important elements of fact, history and philosophy.
So, be wise in your battles. Don't conduct a verbal war - conduct a gentle, peaceful conversation. Scale up the harshness if they are themselves experienced debaters, but always remain civil, polite, giving compliments and encouraging them when they use their brains! Don't stay permanently negative and destructive because their only recourse will be to reject everything you say! Sweeten your harsh, cold truths about the universe with smatterings of social niceties!
Fundamentalists are often immune to both logical arguments, historical facts and psychological pressure. They have self-identified with their religion and fought so many battles over it that they have invested too much time to it to give it up. They no longer know or understand their own true motives, and they can be impossible to deal with. They will often write volumes, have strange ways of approaching problems that defeat reasonable analysis, and are utterly convinced of their own position. Their stance has hardened due to many debates and the chances are they've seen every argument before. It doesn't really matter who debates them, or what 'evidence' their opponents have. These people are lost, and only internal change can help them. Present the facts to them, present evidence, but don't bother arguing.
Crazy people who do not engage in actual debate, but who respond with 'random' rants about random things, write at length, yet don't seem to make much sense. There are lots of these outgoing people on the internet. You may pick up on particular mistakes and reply to them, but you can guarantee they will not listen, and will reply with reams of waffle, often using words in strange ways, completely abandoning logic, and using lots of CAPS LOCK. Do not waste time on these people.
Those who do not learn are not worth it. Some people simply cannot be educated - not because they're too indoctrinated or crazy, but because they do not know enough about the world, and are incapable of figuring stuff out. They will lack all knowledge of science, maths, probably struggle with written English, and resist all attempts to teach them stuff. Think about what exactly the point of arguing with these people is. Telling them to read a book on a relevant topic is often akin to insulting them. Insult them, and move on.
I detail the wider sociological factors that are undermining religion on a page on www.HumanReligions.info, "Anti-Religious Forces: Specific Factors Fuelling Secularisation" by Vexen Crabtree (2011). Get in league with the representatives of these movements and ideas! The menu of that page is:
The single biggest step, possibly unlikely, is to tax the Church on all its income, property and land and watch it instantly fold up to a fraction of its size. Charity is a good cause, but Church is not the way to do it. Support taxing of churches, demand it, and make it known that good people will continue to do good work whether or not they have the "charitable" backing of a church. Nearly all religion-based charity work is a backdoor method of evangelism, and at worse, a subtle method of outright extortion, with most money going to pay the wages of churchpeople. It is all more efficient it charities are run by secular, non-religious folk, who have no church overheads or expensive cathedrals to maintain!
Women, LGBT communities and minority religions - as well as competing denominations - all must unite in order to topple the horrendous dogmas of established religions. The problem is, when one falls, another rises in its place. So the true battle must be fought against establishment religions in general. Warn people about the horrors that occur when religious dogmas are enforced alongside civil law; the more power the ruling religion has, the more the minorities and others have to lose. Stonewall, Human Rights bodies and many other campaigners have all fought long battles against Christianity and Islam; embrace these bodies in the fight against tyranny and delusion. The more members these defenders have, the more governments are likely to listen to them in their fights against religious oppression.
Forums and usenet are the best place you can practice, hone and perfect your arguing techniques. Some of these will remain archived for decades to come so always be respectful yet forthright. You will learn to be precise, to think quick and to read around the subject area because people with all sorts of specialities will be arguing with you. Practice with this will make you knowledgeable in a practical, real-life kind of way. Join Christian mailing lists and engage in arguments. Ignore the fundamentalists once they stop being logical, and stick to what we do best: Logic, historical facts that contradict religion, philosophy and common sense.
Work alongside a friend who is constantly looking to point out your mistakes in logic and fact, and who you sit with whilst debating. Do not argue when you are clearly wrong - publicly admitting someone has come up with a good argument will give you respect and make others more likely to listen to you, and to be civil.
My own websites have achieved much in the way of educating people, bringing people out of delusion, and helping other debaters attain the same goals. Creating a simple website is easy and free. Approach the content in a few ways:
Create a site with a religious theme and title. As there are already many good, skeptical websites out there, with a wealth of important information on them, simply link to them. Then, at the very least, you have aided the effort of others again skepticism against wishful thinking and delusion.
Investigate one area of religion, or, one particular belief, or one particular event in history, and analyze it from a sensible, thinking, skeptical point of view. Link to more general websites on this page. Become an expert, or at least respected, as an author of that particular page (or pages) on that particular subject. Mastering one tiny field is always a promising beginning!
If you debate lots online, then, document some of your best clashes, and turn them into a webpage. When similar arguments arise, you can use your own published notes to aid yourself. Over time, you can build up a knowledge base which others will also find useful. This was the beginning of my Bane of Monotheism website.
Over time, your creation can blossom - or it can sit there and simply provide some links to other websites, helping those sites prosper. Plenty of advice on how to build websites is available online.
It is gratifying to be able to change someone's opinion, or to defeat them in an argument. Arguing on usenet, when done properly, is not a waste of time but a strong source of confidence and experience. You will become familiar with your own weaknesses and develop good textual arguing skills - as long as you avoid hot-headed counterproductive personal vendettas!
Arguing with street preachers, promoting occult religions and having a knowledge of theology will aid you, along with your reputation and image, in gaining an air of authority when you speak to others. Usenet is a good place to learn to use speciality words easily and quickly. And the argumentative atmosphere makes it a much more challenging and stimulating place than other methods of learning that are devoid of such in-your-face competition.