I became a liberal Christian round about the same time that I became a liberal everything else: college. Growing up on the mission field had ironically sheltered me from Christian culture, and the full-on blast of it I got at Oklahoma Baptist was my first real crisis of faith. When I described, a few entries back, "the type who would condemn my arrogance for claiming to have written myself what I had in fact written while ascribing the excreted flotsam of their stream-of-consciousness to the transcendent creator of the universe" I had in mind several quite specific acquaintances from precisely this period. Round about that time the extremist fundies took over the mission board, Bush took over the government (much to their delight), and I found out that--oh wait: the Earth isn't 6000 yrs old.
So: evangelical culture was shit, and the evangelical leadership were slimy, power-hungry turds who slandered and fired missionaries, supported wars of aggression, and lied to children (me).
Clearly much of what I had grown up with was vile nonsense, but if I could excise it from Christianity, something might be saved--I became a liberal. But once you begin to question--once honesty and circumstance have forced you to reevaluate your beliefs, you can't just stop. Yes, going liberal had freed me from the contradictions of literalism, but ... I still had questions. Questions about certainty, for example, or about evil, for which there were no satisfactory answers, which eventually lead me to prefix 'Christian' with 'agnostic', and finally to drop it altogether.
Creationism is patent bullshit, but once you've finally gotten over that, you then have to ask: what about theodicy? Inerrancy is bunk, and incompatible with a loving God, but abandon it and how do you know what you claim to know about faith? Once you cross the line and realize that some of what you believed just isn't true, your thoughts inexorably turn towards the rest. You have to know what is true and what isn't; you have to have answers. The liberalism that I adopted to try to save my faith failed me; if I had started there, then I might not have fallen, but falling from where I did I just crashed on through.
In my line of work, I was inescapably confronted with the problem of evil. I worked with children--many of them handicapped--and watched all of them suffer and many of them die. Is the free will of a sadistic murderer/rapist more important to God than the life of a child--including all the free will that her killer robbed her of? And if God so values free will that He doesn't act, then how can you tell the difference between a God who does not act and one who does not exist? Do we just not understand Him? Then how do we know that He is good--and what would such a word even mean when applied to an incomprehensible, omnipotent being who lets children be raped and murdered for His own inscrutable reasons? Did she just deserve to suffer? The very suggestion is monstrous--and this is what I mean when I call Calvinism a bad-god religion. Did Christ on the cross suffer alongside her? So God is one of those assholes who show up at orphanages and get all weepy-eyed while accomplishing fuck all? Let's hope not.
I don't have a degree in theology, and there's certainly more to it than just theodicy. But I've read a lot, and I've never heard a satisfactory answer to that question. I abandoned 'check you brain at the door' Christianity in undergrad, but the kind of belief that I tried to forge from its ashes didn't satisfy, either. I've heard Hitch and Dawkins criticized for dealing with the 'low end' of Christian thought and ignoring the high end, and I've had an equivalent criticism leveled at myself. But the questions which made me leave weren't answered by the high end any more than the low: true, the high-enders don't think that the craters on the moon were caused by Noah's flood*, but they still assert that an omniscient, omnipotent, and omnibenevolent God runs the universe. That raises a lot of obvious questions, and you don't need a degree in theology to figure out that if anyone had convincingly answered them, you'd have heard of it by now.
*I really, really wish I was making that up.