This is a question I've always batted around in my head.
If a man sodomized little children all of his life, then... say... intentionally flew his fighter jet into a bomber that was about to drop a nuke on a town to blow it up... is he a good guy? My gut says no, but he could have flew off and saved himself. He did not have to give up his life. He could have escaped. But he chose the way he knew would save the town at the cost of his life. Is that worth more than the dozens of lives he ruined?
It's a hard question, so I tend to try to look at the reverberations of the polices that will echo in humanity's time line. Those dozens of lives are valuable, sacred, and should have never been ruined. I could never forgive that. I can be glad the town is saved. I can acknowledge his role. Hell, I can even admit it out loud what he did. But an evil man doing one (massively) good thing does not erase how he chose to live his life.
He chose to do one great thing with his life. Thousands will live because of it. He has affected humanity in a positive way with his action. But he's still an evil man. I can't logically weigh dozens to thousands of lives, but that's the morality of good and evil. It is arbitrary.
If a man was a saint all of his life, and then one day lost it and beat a woman, is he still a saint? Even in this example, morality that we were all taught makes me want to revile the guy, but then the 'we're all human' factor kicks in. I don't forgive him for beating a woman, and I might not even like him personally after finding out about it, but I'm somewhat ashamed to say that I might be willingly to listen to him on why it happened.
If he was drunk, high, out of his mind with grief, something that vastly separated himself from his normal beliefs and functions that made him do such an act, I could possibly start to try to understand better. But even typing that, my mind is saying 'Bullshit'. But I want to believe what I typed because I know I'm human. And while I can revile the idea of every hurting someone, especially a woman, I know I have my own limitations that someone can try very damn hard to cross.
And I think that's at the crux of the matter. The 'Human' Measurement. How much can you willingly put aside because it's human nature to make mistakes. There's a tipping point from 'Only Human' to 'This guy's kind of a dick' and it just falls from that point on.
And what makes this so hard is that is a Measurement that's different for every human being. What might still be in the 'Oh, he's only human, he'll make mistakes' category for you might have been past the 'dick' phase for me, and going straight to 'Despicable'. Until we all develop the Hivemind the governments have been working on, it's going to make us split on how much we can hold someone's achievements away from how they lived their lives.