From what I can tell, Puck's basically got the right idea here. I can only speak from personal experience, but every "confrontational" type of atheist I've met over the years has displayed something similar to the following beliefs:

- Absolute truth exists.

- Fundamentalist interpretations of religious doctrine are the "purest", or most definitive, form of that religion.

- The religion's teachings irreconcilably clash with the more valid "truth" that's been uncovered through scientific study.

- Either or both of the following: It's morally wrong to let people exist blind of the truth, and the religion's false doctrine is restrictive and/or damaging to society as a whole. (In addition, many seem to have a personal grudge against the church based on personal experience, whether they're willing to admit it or not.)

Thus a perceivably dominant and flawed belief system like Christianity must be opposed. That's the mindset of the most militant ones I've met, at least. Most atheists - including most of the ones here, I'd bet - don't particularly care about Christianity one way or another; they just feel persecuted when questions like these are leveled at them (which they are, to a certain extent) and get defensive about the subject in response. The ironic thing is that a lot of the Christian side's involvement is reactionary as well, in response to what they see as a deliberate effort by the secular forces of society to marginalize the importance of religion in everyday life (which is also true, to a certain extent).

There's your answer. It's a little disjointed and longer than it had to be, but whatever. I tried. F3 makes a good point in that it's probably not worth discussing any more; knowing this place, it'll just degenerate into Serious Business as usual.