The requirement of faith to avoid Hell is the least moral part of Christianity, or at least those forms of Christianity which preach Hell. For the purposes of this post, I am assuming a doctrine of Hell wherein those who either do not believe in Jesus or do not follow him are condemned to Hell; I am also assuming that Hell is a place of eternal torment.
It is immoral in Three distinct ways. First, many of the common ways in which various Christian sects claim people are condemned to Hell are outside of the condemned person’s control. Second, not every wrong action is as bad as any other. Third, no finite action is worthy of infinite punishment. Let’s explore these more closely.
Many of the common ways in which various Christian sects claim people are condemned to Hell are outside of the condemned person’s control. If people go to hell for lack of belief, it is god’s responsibility to show some evidence; otherwise, he is damning people like me for being how he made them. If people go to hell for homosexuality, god is literally damning them for how he made them. Further, many parts of Christian morality do not always make sense outside of Christianity, such as commands against pornography or abortion or drunkenness. Given this, people could easily be condemned to torment through no fault of their own for not having a reason to follow that morality because they could not see evidence that Christianity is true. Here, again, it really is god’s responsibility to provide evidence either for Christianity or for the morals thereof; otherwise, he is damning people for something outside of their control.
Not every wrong action is as bad as any other. A little boy lying about brushing his teeth is clearly not as bad as Hitler, but under many forms of Christianity, they both warrant eternal punishment, as both are sins. Indeed, by some forms of Christianity, the little boy has no chance at Heaven unless he gives his life to Christ, even if that is the only bad thing he ever does, while Hitler could have gone to Heaven if he experienced a deathbed conversion. According to some apologists, the guy who simply can’t see any evidence of God’s existence but follows Christian rules (perhaps because he somehow sees them as the best code of ethics) is as deserving of eternal torment as the guy who brutally murdered millions. If you really believe that any being who cares for his creations would consider these things equal, you’ve understood nothing of justice.
The Christian can easily bypass these two flaws while maintaining a belief in Hell by believing that god, being perfectly just, would never condemn anyone for anything outside of their control. An atheist could still argue that an omnipotent, omniscient god can not co-exist with free will in his creations, but I have no interest in making that argument here.
However, the third way in which Hell is immoral is much harder to escape: no finite action is worthy of infinite punishment. The little boy who lies about brushing his teeth might deserve some punishment if caught, such as being forced to brush his teeth for twice as long as usual. A person who steals an object is commonly forced to return it and perhaps pay an additional fine; anything more is typically considered unjust in our legal system. A person who commits murder might face a lifetime of imprisonment or death, but we would not consider torturing them through burning then healing, gradually burning more and more of his body until he eventually dies, to be moral. Indeed, if someone suggested such a punishment, we would consider them immoral. Why, then, is torture by burning, not just until death but eternally, moral when it comes from a deity?
The Complete History of the Universe: A Personal Journey 