No one has ever said that only SJWs get offended by things. However, there is a difference between being offended by something and moving on with your life, and being offended by something and actively spreading hatred and going after the person who caused you that offence.
The impressionable part is true since a large portion of his audience is young and will copy him. So I'll give you that. However, him apologising isn't going to stop any of them from still copying him. Doesn't matter what he says or does, the fans of his who actually will copy him are largely the same people who are just going to think he's giving in the PC culture. I actually think him apologising will cause certain parts of his audience to start calling other people niggers even more often, simply because they know it bothers so many people.
White people cared more than black people did. I saw far more white people being overly vocal about what happened than I did black people. A large portion of the black people I saw upset over it were SJW types who you'd get that response from over anything. I actually saw almost as many black people defending him as I saw condemning him. I don't think black people really care - and I also don't think they should care. This is a non-issue. We don't need to be making a big deal out of it.
What part of the argument is black and white? The only part I see that's black and white is when people say "If you say the word nigger then you are a terrible person regardless of context". That's black and white. Because you're saying that if you don't say the word, then you're okay, but if you do say the word, then you're bad. That argument doesn't take into account context, intent, or any other possibility. It makes it a black and white issue because there are only two possible sides - racist or not racist. It's not black and white to say that saying nigger isn't always racist or bad, and that's what the majority of people defending PewDiePie are saying. Sure, people who think that nigger is an appropriate word for any circumstance no matter what and if you get offended by it then you're a dumb SJW are also putting forth a black and white argument. But those people are in the minority.
Most people are saying one of two things:
That no one should ever use the word under any circumstance - this is a black and white argument.
That context and intent matter and that just saying a word isn't bad - this is not a black and white argument.
So I really don't know what you're talking about by mentioning a black and white argument since you're clearly not referencing the people who think it's bad no matter what. And honestly, I don't think he did anything wrong or bad. Did he do something I probably wouldn't have done myself? Yes. Did he do something that I would probably advise not to do? Also yes. But did he do something that I condemn and has given me a negative opinion of him? No. I really don't care that he did it, and I honestly don't think we even need to be having this conversation. I truly do believe that it is a non-story. People can be upset all they want, that's their right, but there is no need to be screaming about how he's a terrible person all over social media. Just be offended, then move on. There is absolutely no need for the reaction this has gotten.