If you look at the night sky you'll see more dark areas than points of light, but you still use those points of light and the contrast to define what brightness and darkness is. That would hold even if there was just one visible star besides the sun in the whole universe.
> I probably already engage in acts that future generations will consider evil
It's nothing to do with new insights coming about. If for example you reap the benefits of wars of aggressions and don't speak out against wars of aggression, what future generations think of it doesn't matter.
When you see a homeless person sleeping in the cold, and you put a warm blanket over them and they don't wake up and nobody sees it, was it a good deed? I would say yes. It will even remain a good deed if you yourself forget about it.
So why would that be different for bad deeds? It can only be bad for reasons that are present at the time. If someone is getting deceived it's hard to blame them. But if someone is ignorant because they made many little choices to remain ignorant, it's different. If someone couldn't have possibly known because of scientific discoveries made later, it'd be silly to "blame" them. But that's hardly relevant to the Holocaust.
And nobody "statistically" does x murders and y good deeds each year. We do nothing statistically, we just do what we ourselves actually do.
> Of course, the terrible things I heard from the Nuremberg Trials, about the six million Jews and the people from other races who were killed, were facts that shocked me deeply. But I wasn't able to see the connection with my own past. I was satisfied that I wasn't personally to blame and that I hadn't known about those things. I wasn't aware of the extent. But one day I went past the memorial plaque which had been put up for Sophie Scholl in Franz Josef Strasse, and I saw that she was born the same year as me, and she was executed the same year I started working for Hitler. And at that moment I actually sensed that it was no excuse to be young, and that it would have been possible to find things out.
-- Traudl Junge
While we might "pity" people in the past for not knowing many things, moral judgement has to do with the options someone has. Even if the majority is using their options badly, that doesn't mean those options didn't exist, just like there being less stars wouldn't make the rest of the night sky brighter.
> The sad truth is that most evil is done by people who never make up their minds to be good or evil.
-- Hannah Arendt