The doctrine of eternal damnation is one of the most wickedest teachings ever imagined by humans. If Jesus did indeed exist - which is debatable - then this deranged, lunatic, preacher seems to have thought it fun to create this idea and scare the "hell" out of people. The Old Testament, reeking with violence, cruelty, barbarism and intolerance as it is, soaked with blood as it is, gives humans final peace after death. But no, gentle Jesus meek and mild wanted to get a kick out of damning people to eternity, it seems. Not even the dying moment of a person would now be peaceful.
After all, what justice is there when someone is sent to eternal damnation? If I were God, even the most appalling mass-murderer would not be sent to eternity in hell - nobody would, in fact. What can be achieved from it? Nothing useful. I want people who have done wrong to understand what they've done and genuinely be remorseful for it, not to watch them roast for the sheer pleasure of it. Is it not unjust to give a punishment that lasts infinitely for a crime committed in a finite time? Doesn't this make God ( or is it Jesus, if it is his invention? ) infinitely wicked and unjust?
A particularly vile thing among many Christians is that it teaches this doctrine to children. Is it not extremely immoral to tell something like this to children? To tell them that some people are going to be thrown into a lake for fire and are going to burn, screaming for eternity? And what happens when the child realizes that there are many loved ones around her that are going to burn in hell forever? Imagine the damage this kind of thing does to the delicate mind of a child.
Another group that has suffered from this is gay people. After the initial attempts to change one's sexuality, and failing to do so, to the Christian who realizes that he is gay and that he is unable to change this, the road to hell is pretty much secured in his mind. You can find plenty of messages on forums, with the same basic message - "I can't help being attracted to men but I don't wanna go to hell - Please help me". What evil! To prevent someone from falling in love, to snatch away a unique and magnificent experience such as love from someone - I would say it is the unforgivable blasphemy against a human - and Christianity is certainly guilty of this.