It started with this exchange with a Christian, Robert, in comments to a previous post.
PZ: if your reason and faith come into conflict, which will you choose to discard?
Robert: Reason every time, only a fool wouldn't.
Robert goes on to elucidate.
Reason is a tool; faith is life - now you tell me what's more valuable. Reason itself tells one to dispense with reason here. ... salvation is offered to a PERSON, not just his intellect. Think about it: why would God want to save only a part of one? You ... are an emotionally retarded reason worshiper, as are all atheists and God-haters... Moreover, you have yet to force the above choice upon me. I resolved the apparent contradictions in my account.
An interesting comment: 'faith is life'. We all have faith of one kind or another. For example, I have faith that the Christian hell is not real, although I can't prove it. This doesn't conflict with reason but it isn't perfectly justified by reason alone. I just find believing in hell impossible, almost physically offensive.
I think human beings live in an intolerable circumstance. We live, but we know we must die, we have hopes for the future but almost all of them (of necessity) must fail, most of our potential is wasted, and the world is full of suffering. Yet we have to go on. So here is my definition of faith:
The beliefs we have to have, just so that we can carry on living.
And that's why 'faith is life'. If I thought that people were really burning in hell, I couldn't carry on living. No doubt for a Christian the thought that his existence, his selfhood, will cease to be in a few decades is similarly intolerable. I don't have proof of my faith, but I can't discard it, and for the Christian presumably the same is true. Faith is driven by this necessity.
Other things I have faith in - that the world is real, that other people are real, that the world has some reason and regularity to it, that kindness is worth it - and so on, loads of beliefs which aren't against reason but aren't utterly guaranteed by reason.
People obviously then add a freight of other beliefs (good and bad) onto that core engine of necessity, and you end up with a big baggage of food taboos, creationism, politics or whatever.
I think to be most healthy, people (including atheists) should probably try to see how much of their 'faith' is just baggage of this kind, and how much we really can't shift. I think once you get to that core you won't make somebody change. And that's why I think we have to just pass over other people's faiths, and accept them, because it is life to them.