It boils down to this...
When someone does something stupid, I mean REALLY boneheaded, and he doesn't receive immediate punishment...that person will go on to do terrible things in the belief that everything is fine and NOTHING could possibly go wrong. When he DOES get punished, he has to rethink his life. And if he doesn't get to live...well...sorry, but rhinos probably kill small animals every day. They only do it because they bug the hell out of them.
People are behind the Casey kid not just for the chutzpah, not just because it was cool. Okay, some probably are, but some are also calling it justified as well. Apparently, when you're the target of enough ridicule and you can't stand it anymore, you'll want to do things. Makes sense. There's someone we all want to strangle, I'm sure. In this case, a wimpy 10-pound kid decides to put on the tough act.
He did this to a guy who was bigger, stronger, and currently pissed off at people pulling this sort of shit. And the Casey kid didn't do anything at first, either. Then, hitting actually occurred. Talking garbage and baiting and punching. Finally, the dumb kid gets shown exactly what he's messing with, someone who can end him in one move. Enough was very much enough. I wish all that stupid were taught a lesson so clear.