Robin Williams at least cut people checks. IMO that takes a good person and good heart. Dude was a powerful force in comedy for years, even on the come-up he was filling up rooms. He could have stolen their shit and told them to fuck off. And he was so fucked out of his mind on drugs you can kind of forgive him. His original material was great so I would be willing to give the benefit of the doubt to him that he didn't steal jokes from other comedians intentionally.
Stand up is tough, you start flying by the seat of your pants and you're so full of adrenaline/anxiety on stage that suddenly morals go out the window and you will almost do anything to get that laugh. I've never stolen a joke myself but I know a comedian who tells my favorite joke of all time and he is almost an unknown, I first heard his joke when he was just rolling in the open mic scene in Toronto. I wish his fucking joke was mine. It will never be though. I do like to tell people that joke at like parties and credit it to him, however. Comedian's name is Graham Kay.
Anyway, IMO as long as you admit it afterwards, try to explain yourself, apologize, and attempt to make restitution you can be forgiven, which is what happened with Williams. Dane Cook, Amy and Mencia all denied it even though it's right in our faces - and it appears Trevor Noah does too. He should at least admit his joke is very similar to the Russell Peters bit.
As for Peters, his white-kids joke that he stole from Eddie Murphy, he never seems to have been called out on. I actually suspect Paul Mooney wrote the joke for Eddie because he worked with both Eddie and Peters on their big specials.