I blame it on the 2004 election.
One of the things I did that year was participate in a debate community about the Presidential election populated with some crazy Republicans, a few sane Republicans, various stripes of liberals. One of the things I took an interest in being in that community was good logic and argumentation, and in particular, the kinds of fallacious arguments proposed particularly by the crazy Republicans, and a few of the extreme liberals. Both so that I could defend my arguments as well as punch holes in theirs. I bought books and lecture series to further my knowledged base, in addition to just watching others whose opinions and logic I respected. Some of these people became online friends on my personal blog, and many of the most rational of these turned out to be atheists.
After that community closed in the wake of the election, I started trying to apply good logical principles to every online debate I engaged in. And I found that I was appalled at the irrationality of many of the people I encountered. And not just that, but their unwillingness to rethink their conclusion or, more particularly, the basis for their premises. My accusing someone of being rational is not so much an attempt to change their mind, but at least force them to justify their beliefs better. An intellectually honest person will change their beliefs if they can find no good justification, but that is secondary to getting them to think about their conclusions more clearly.
It is partly for this reason that I reject the charge that is so often leveled at me, that I think people are nuts or irrational or intolerant or whatever, if they don't agree with me. Rather, I expect that people will disagree, as they have different priorities than I do, but I expect them to acknowledge that basis for their beliefs. With respect to religion, if truth doesn't matter, but belief does, then I want them to accept that. If truth matters more than belief, then certain other consequences follow from that than blind obedience to religion.