Here are a few of the reasons I think Christianity is false. Note that some of these apply only to rabid fundamentalist versions of Christianity, while others are more general. — RWD
Neurophysiology makes a strong case for the non-existence of anything like an immaterial soul. If personality resides in the soul, then how can drugs and brain damage affect it?
What is it that makes people believe in God at all? It seems to me that gods were invented by men to explain things they didn't understand. But we understand a lot more today (though of course the frontiers of science are always speculative). Given that it's impossible to have an explanation for everything (because then that explanation would demand another explanation — "But Mommy, why is it that way?"), why not just take the universe as we find it, rather than positing some incredibly complex cause for which we have no evidence?
Science has shown the stories of creation and the flood to be false. (See the talk.origins FAQs.) I'm aware that many Christians have no problem accepting evolution, but for me it demolishes the most important argument for the existence of God. Not to mention the verbal, plenary inspiration of the Bible.
Why was "demon-possession" so common in Jesus' time, but hardly mentioned at all in the Old Testament, and apparently non-existent today? Modern medicine seems to have transformed demons into things like epilepsy and schizophrenia.
There is no justification for eternal torture in hell. Unremitting revenge debases those who practice it. (I have no problem with God snuffing people out of existence, but hell as described in the Bible is sadism.)
How can people be happy in heaven with loved ones in hell? Some say that God will take away their memories, but there are at least three problems with this: (1) this would be a huge violation of our rights; (2) by so doing God would tacitly admit that hell is wrong; and (3) in the story of the rich man and Lazarus, everyone's memories were intact.
Christianity asserts that more than 50% of the people in the world will go to hell. ("Strait is the gate, and narrow is the way that leadeth unto salvation, and few there be that find it.") This belief is morally repugnant. Surely an all-powerful God could have set up something different.
In the Old Testament, God ordered the genocide of the Canaanites, including infants. (In some cases he allowed them to keep the young virgin women alive — Numbers 31:17-18.) How can this be reconciled with the idea of a just and merciful God?
The Bible does not plainly and unambiguously tell us the single most important thing we supposedly have to know: how to be saved. As evidence, I submit the many Christian sects which disagree heatedly on this point. In one place it says, "Believe on the Lord Jesus Christ, and thou shalt be saved." In another, it says, "Faith without works is dead." A few sects believe that if you're not baptized you'll go to hell.
The plan of redemption makes no sense. There are several theories about why Christ had to die, and all of them are unintelligible.
The stories of the resurrection are not consistent.
It is unfair that some people (Thomas, for example) should get convincing physical proof of miracles while the rest of us are supposed to believe on hearsay.
Why did God design the world so that some animals have to eat meat? Why did he create parasites? Why do innocent animals suffer?
Why did God create so many species only to allow most of them to become extinct before man even existed?
Matt. 16:27-28: "For the Son of man shall come in the glory of his Father with his angels; and then he shall reward every man according to his works. Verily I say unto you, There be some standing here which shall not taste of death, till they see the Son of man coming in his kingdom." Jesus thought the end of the world was coming within one generation.
There is no good reason to believe the canonical books of the Bible while rejecting the apocrypha. The canon was only gradually agreed upon, and finally formalized by a vote. Early church fathers quoted extensively from apocrypha.
Most people believe the religion of their parents. If one and only one religion is true, why did God not make it obvious to all nations alike?
Even if there is a creator of the universe, why does he want to be worshipped? God is an egomaniac?
If God wanted us to have free will, why does he threaten us with hell? It isn't free will if you've got a gun at your head.
Romans 9:15-23 says that God deliberately causes sinners to sin. (For instance, he hardened Pharoah's heart.)
There is evidence inside the Bible itself that much of the Old Testament was not written until the time of Josiah. (II Kings 22:8+, in which the book of the law is conveniently "found" in the temple, and contains some laws that apparently nobody had ever heard of before).
