One of the most important rules in warfare is "know your enemy." This is the main reason it is a good idea for atheists to read the bible. I'm not sure what the situation is like on other continents, but at least here in North America, Atheists seem to have a tendency to be drawn into debates when they reveal that they don't believe in God. I believe this is because some Christians feel that the atheist should be obligated to justify his or her beliefs. Another military maxim that may or may not be true is that the best defence is a strong offence. I'm not too sure about that, but it seems to have worked well in the fire bombing of Dresden.
Anyways, a good way of justifying your own beliefs, of lack thereof, is to explain, using evidence from the bible, exactly why you don't believe the same things that they do. If you can point out things such as the radically different behaviour of a God who is supposed to be perfect, and thus by definition, cannot change. Or perhaps the fact that Luke 3: 23-38 and Matthew 1: 1-16 cannot even agree on who Jesus’ grandfather was, let alone any of his other ancestors. Once you have proven that at least part of the book that is supposed to be perfect is false, you can then raise doubts about every other damned thing in there.
They may still continue to argue, perhaps saying that while the facts might be a bit inconsistent, the main message of love remains unchanged. This is when it's time to go in for the kill. The bible is filled with instances where the main characters, or even God himself, act in a manner that most decent human beings would find reprehensible. A few examples include the time God killed off every human being on the planet except for one guy and his family who "found grace in the eyes of the Lord." Or the time god sent two bears to kill 42 children because the children called Elisha "bald head." Or the time that Lot's daughters got him drunk and slept with him, both getting impregnated. The list goes on, it's a large collection of books, and it's filled with examples.
But then again, if you are too lazy to actually read the entire thing, the wonderful internet is filled with tools that catalogue and index funky stories from the bible like these, and a bunch of other contradictions and depraved acts.
Disclaimer: While belittling someone's religious beliefs can be fun, one should take care who they use it on. Done successfully, what you could be doing is completely destroying someone's view of how the world works, leaving them only with the bitter realization that death is inevitable and in the long run, life is void of meaning. Woo Nihilism Baby! People disagree on if this is a good thing. Is truth for the sake of truth better than lies for the sake of happiness, comfort, and hope for life after death? Frankly, people would be happier believing in the big spirit in the sky. You were happier when you thought that Santa brought you presents at Christmas. Is that happiness justification enough to allow people to continue believing in Santa, God, or whatever it is that gives them their kicks? The choice could be up to you, but since people might resent you for doing so, I suggest you try not to do this to family members and other loved ones. Maybe even just stick to people who piss you off.
Ok. If you do ever get into a debate with a Christian who has made a point of studying the bible, and theology in general, I rather doubt I can help you there. You best resource would probably be the Skeptic's Annotated Bible, currently located at
http://skepticsannotatedbible.com
The thing about debating someone who has studied it, is that they already know your objections, and already have something prepared to counter it. It may or may not be a good counter, but let's face it, when we're debating about something that needs to be taken on faith, logical arguements get ignored, or some excuse is made up. At the best, with these people, we can point out some of the inconsistancies in the book, force them to admit that some parts of the book may not be true, and *might* be able to get them to admit that other parts of the book, parts more important to their claims, may also not be true. After all, if the Gospel of Mark and the Gospel of Luke cannot agree who Joseph's father was, then at least some part of one of those books is incorrect.
And, if one part is incorrect, it's probably safe to assume that some other parts are incorrect. Maybe Jesus didn't walk on the water, maybe he just gave a talk by the beach. Maybe he didn't rise from the dead, maybe he just got taken down from the cross too early, before he had died.
Defeating people in structured debates wasn't the point of this writeup. I don't go out of my way to convince people they shouldn't be Christian. However, people do go out of their way to convince me that I *should* believe in god, and his only son. This is what pisses me off.
Therefore, when someone comes to me spouting off nonsense about how God is all loving and holy and stuff like that, I really do prefer it if I can have a few examples of how the BIG MAN himself has acted in not so nice of a fashion, or how his appointed PR reps on earth have been rather despicable.
When I have someone come to me and tell me that homosexuality is an abomination to God, because Leviticus tells them so, I want to ask them if they still make a habit of sacrificing animals and burning them to please God, like it tells them to in the first chapter of that same book.
I don't give a shit about formal debates. I only care when other people's religious beliefs adversely affect my life, or the lives of others, either through personal interaction, or passing of legislation based upon it. I mean, homosexuality is still illegal in how many states in the US? And why? Eh, I think you get my point.