People sometimes ask why I don't believe, and the honest answer isn't a single knockdown argument — it's a way of deciding what to trust, applied consistently.
Science is the method I trust, and it rests on a couple of assumptions I accept for practical reasons: that there's a real world outside my head, and that there are truths in it to be found. Grant those, and science turns out to be unique in one respect — it accumulates. Educated people all over the planet, across every culture and language, converge on the same findings and build new ones on top, and the whole thing throws off working technology as a byproduct. I don't know another tradition that can say the same. It's also the only one I know that can be turned on itself: its facts and theories are always up for revision. Religion can examine itself up to a point, but eventually it reaches a dogma that can't be questioned — you either accept it or you don't.
When I hold other paths to truth up against that, none of them feel right. Most borrow science's reasoning for a while and then, at the critical moment, swap in a fallacy. The one method I genuinely can't dismiss is raw subjective experience — "I felt God," "I saw a ghost." I can't disprove your experience. But I also can't verify it, and neither can you, to anyone else. If I myself had a vivid experience with no physical trace, I'd be obligated first to look hard for a natural explanation, and if I couldn't find one, to set it aside — because by Occam's razor the simpler account (that I was mistaken) almost always wins. Even a thousand people sharing the same experience doesn't get you there; shared illusions and suggestion are real and well documented. Anecdotes, however many, aren't evidence. They're a reason to go looking for the cause, not a substitute for finding it.
That's the core of why I can't accept Christianity in particular. From a skeptical standpoint there's barely enough to establish that Jesus existed, and nothing like enough to establish the resurrection. Extraordinary claims require extraordinary evidence, and the evidence on offer is subjective and secondhand.
Underneath all of this is one real assumption: that everything which happens has a physical cause. I lean on it because the alternative keeps losing. The territory we call "supernatural" has been shrinking for all of recorded history — every force once attributed to a god, from the motion of the planets to the spark of life, has eventually turned out to be natural. "Metaphysical" really just means "not yet explained," and time and again, not-yet-explained has become explained. The last redoubt is the human mind and its supposed soul, and I'd bet that one falls too, the day we build a machine that genuinely thinks.
So I'm left making a modest, almost reluctant assumption: a physical world exists outside of me, and anything that interacts with it — a soul included — is part of the same chain of cause and effect, and therefore part of that same world. From there, my reasons for not believing in Christianity, or any religion, simply follow. It isn't certainty. It's just the most consistent place I've been able to stand.