Killing Hitler wouldn't stop the war or it's horrors. All this would do would be to change the dates when the war started and ended.
If you know your history, rather than subscribe to the "the world can be easily be classified in Black & White, Right & Wrong, Good & Evil, Hitler & Ghandi", then you will know that Germany was forced to take all the blame for the previous World War (as the losers who caused the most damage to France and Britain) and was in the simplest of terms "being bullied" by the rest of the European powers. This caused great resentment towards their lot in life and the rest of the world, throughout the German populace. If not Hitler, then someone else would have taken his place as a warmongering nationalistic extremist (the details are too much for me to get into here, but that specific type of leadership was very appealing to the German populace at the time).
I don't deny Hitler being a madman, an opportunistic warmonger, a racist, and a political extremist. But I am getting tired of him being presented as "the ultimate form of evil". He was a human being, and like all of us he had his good points, as well as bad (Vegetarian Dog-lover, who managed to earn the love of a woman). My belief is that he must have been somewhat psychologically disturbed, in order to actively seek the utter annihilation of an ethnic group and cleanse humanity of genetic variety (At least I hope one has to be, to seek to achieve such atrocities. Then again, he simply gave orders at a distance. So shouldn't we be dismissing the masses of human beings who carried out these deeds as mentally unstable?).