I think that KSI is a bit of a twat, but to be fair to him, he was a dumb teenager at the time and did a thing that a dumb teenager, who's a bit of a twat, is known for shock, dumb, immature humor, has recently gain loads of money and had his ego stroked on the internet, would do. He iirc acknowledged that he did a mistake, apologized, and hasn't been involved in similar controversies from then onwards afaik, so I think it's fair not to hold that against him. It's a bit like the James Gunn thing, albeit worse and he actually was a teenager at the time, in sense that it happened a long time ago, he apparently tried to change and the internet landscape was quite a bit different so how long is it fair we hold that against him?
Can't say I am in anyway qualified to talk about the N-word but "content creators", entertainers, people who are famous for any reason whatsoever, cannot possibly be responsible for being role models. That's just ridiculous to expect. There's a difference between a person and his persona, product, art, etc and it's on the parents to make sure their kids know that.
I still think that KSI is a twat, but some of the arguments you put up are just silly.