Actually, as strange as this will sound, using Augustinian logic, existence is better than non-existence. Therefore, an existing Hitler is better than one who does not exist. HOWEVER, and this is key, every time Hitler does something evil, he becomes less existent. Why?
Evil does not exist per se. Evil is defined as an absence of good. In other words, God is the Summum Bonum, the All Good. When you do something that is less than all good, you become less than All Good, ie, less than God. Humans were less than that already in Paradise, by virtue of being Created things. But, they did not know the difference between Good and Evil, and could have lived forever there as a result, in union with their heavenly Father.
Hitler would have existed. But he would not have been what he was. After humans learned what Evil was, by the commission of the sin of disobedience to God, and were forced out of Paradise, they knew to choose Good or Evil. At this point, choosing evil renders the soul less than All Good, less existent.
Notice that although they had insanely long lifespans, they still died. And eventually, their lifespans contracted to what they are today. Moses lived to be 120, which is what the very oldest of our people are living to be today. As they chose more and more the evil, they became less and less existent spiritually before God, until the Flood, when God eliminated them except for a small number.
After that, starting anew with a small number of people (however you want to interpret that), people still could choose the good or the evil. Using Hitler as an example (by the way; Godwin's Law, you lose [I'm kidding; its actually not a bad example]), his existence is better than his non-existence. He made himself less existent by the evil choices he made. Granted, this is no comfort to the people whose lives he took. But, lets be honest, if it hadn't been him, it would have been another asshole. If it hadn't been us, it would have been some other group.
We aren't the only ones to have ever been "genocided" (to coin a word). We just happen to perhaps have had the largest numbers lost. 6 million IS a hell of a lot to lose. I don't recall any other genocide taking quite that number, although in terms of a percentage, some have taken an equal percentage (or even higher) of the population at which they were aimed.
I think perhaps the craziest was the auto-genocide in Cambodia. What crazy bastard kills his own people, for fuck's sake? That one just boggles the mind. I understand killing other people. I don't like it, but I can at least wrap my head around it. They are the enemy, kill them. But your own people? Holy shit.
Back to my point. Another example. If John rapes a woman, Jane. Jane surely suffers an evil. There is no doubt of that. But John suffers an even greater evil in the philosophical sense insofar as he becomes less existent in his soul. This renders him more likely to do awful things in the future because he is less able to resist the power that evil now has over him, as he is less good. Now, that may not be a comfort to Jane. But it is something to think about.
There is actually an argument in this line of reasoning to be made AGAINST the State using the death penalty. As much as John might deserve it, does the State want to put itself in the position of committing the evil act of killing someone, and thus render itself less existent in its collective soul?
I had to write a paper on that. Having always been pro-death penalty, it was an interesting way to look at it, and I got an A on the paper. Definitely interesting. Anyway, for whatever those thoughts are worth. I have to go. The wife will be home soon.