This is why I like the Halo expanded lore. There's a lot of guilt and grudges when it comes to Thel Vadam in Halo. Dude led fleets that killed millions of humans. He just accepts that he'll never make up for it, no matter how much good he does for humanity after the war.
It also goes into how, even though he was manipulated by the Covenant, he'll never stop feeling guilty. But he's the only Sangheili leader that is 100% devoted to peace with the humans, so most humans aren't willing to take a shot at revenge.