The real irony here, is we are blaming these kids for using a word we, in past generations, have used in hate. "Don't you know how we, your parents and grandparents have used that word? Don't you know the hate and horror we associated with it and how we (collectively, not individually) inflicted such harm with that word? How dare you use it flippantly when we used it so hatefully".
That's really the gist of this. They're being blamed, by past generations, for using a word in fun that the past generations used to suppress the very young man who thought it would be funny to stage this.
The irony drips.
edited to add: before I get attacked by an onslaught of "I guess YOU used that word, I never did", I have to say I grew up on an air force base where racism wasn't expressed. Everyone was the same, and there were no racial distinctions I ever felt or saw. I was in 4th grade (around 1969) when on a trip through rural Mississippi I saw that there were STILL segregated drinking fountains, and liberal use of the N word which I had never heard before outside of literature. Never heard it actually used, and didn't know the meaning of it. Then, moving to rural Texas I saw it a LOT.
So I've never used it. Just to be clear before I get slammed.
edited again to add: oh wait. I did hear it once before, and was too shocked to put it in context and integrate it as a word. I was at a friend's house and there was news footage of dogs attacking the freedom marchers, and fire hoses, and I was amazed at the injustice of attacking apparent peaceful people. So I said why are they DOING that? (meaning the cops) and my friend's dad said "that's just the way "n's" are, honey". I felt like he was from mars.