Quite simply, I read the Bible. I had read the Bible before, but it was only later that I began to think about what the words meant. For example, it's easy for a practicing Christian to gloss over the glaring misogyny, homophobia, hypocrisy, etc. However, being exposed to the internet (especially RF and youtube) brought the bad aspects of the Bible to attention. I realized that to not be associated with the negative things of the Bible, I would have to discontinue use of the "Christian" label. My first step in this process, ironically enough, was to debate in favor of Christianity and try to demonstrate that it was scientifically and logically viable - however, in attempting to do so, I slowly, perhaps subconsciously at first, began to realize that doing so was impossible. For me, truth was more powerful than faith - unfortunately, in most others that are placed in a similar position, this is not true. Once I got rid of that label, I realized I was no longer obligated to avoid questioning certain ideas, and thus what remained of my religion quickly fell apart.
Nowadays, I am essentially an agnostic maltheist - I do not know if there is a god, but I live my life as if I'm operating a one-man resistance force against the (evil) Christian god. Most arguments against anti-theism revolve around other religions being different than Christianity - this is currently irrelevant, as most of, if not all, of the religious people I encounter here in the Bible Belt are conservative Christians. Other religions will not concern me until they are a threat, at which point I will presumably hate their gods as much as I do the Christian god.
Further, while this is less of a concern to me than the moral aspect, many ideas presented in the Bible are, quite frankly, impossible. The Flood Story is one of the best examples of this. I assume most of you already know the details of why the Noah story could not have happened the way it is portrayed in the Bible, so I will not go into this. Knowing that reality and the Bible are in conflict, one is presented with a choice - do you believe in reality, or do you believe in the Bible? Many atheists here would remind listeners that reality can be felt, observed, tested, repeated, experimented upon. However, my experience as being a fundamentalist Christian in my youth reminds me that this is entirely irrelevant to Christians - when your faith is strong enough, your brain simply won't naturally be able to process ideas that you subconsciously know would endanger your faith (I forced myself to read through atheist arguments in an effort to find holes in them, which I ended up never finding), and many Christians seem to hallucinate the "presence" of God and his "Holy Spirit."
In effect, what you get is two different groups living in separate realities - one in the conventional reality, and one constantly and thoroughly convincing itself that life is run by God and not reason (there are, of course, other groups in real life, but we are only referring to the conflict between Christians and secularists). Obviously, these two groups are different, and as I realized a long time ago, two things cannot be different yet at the same time equal - for there to be differences, one option must be better than the other, otherwise they would be the same (which option is better may vary depending on the intended purpose, but there is almost always a superior option). This is why I as a non-Christian feel a moral obligation to bring others away from Christianity - my reality is more reliable than their reality is, because mine is consistent - "God" relies on faith, and since God is theoretically a personal, living being, if there were actually an omnipotent god running the universe rather than science, we would have no order, because while the laws of physics are constant and do not change (having no supernatural source), God could change his mind on something whenever he felt like it. Thus, if the universe WERE run by an omnipotent god, we would be unable to effectively predict what our environment would do to us, unable to determine what makes sense and what doesn't, and we would constantly live in fear of what God would decide to do next. It is far better to have a System in place, one that we could learn and comprehend without fear of it spontaneously changing on us. With reality, I can confidently say that the sun is hot, 2+2=4, and the seas are filled with liquid. With God, anything is possible.
(I suppose a simpler comparison could be made like this: Would you rather live in a country ran by a dictator who's laws he could change on a whim, or would you rather live in a country with a constitution and a formal process for lawmaking?)
This is why we have a moral obligation to convert Christians - they are essentially an element of disorder in the world. We pity them because they are affected by our reality regardless of their belief in it, and we fear them for the impact that their beliefs have on our society.
[/weird tangent]
