The guy seems like a real idiot, but expelling someone from the university is going too far. I'd have to know the context of the Facebook conversation. Was he only talking about rioters who committed the crimes of murder, attempted murder, assault, battery, criminal damage to property, etc.? Even if so, it's a really stupid comment, but I think it was clearly meant as a (bad) joke. He deserves to be ostracized. However, Shaun King is one pretty big POS. He's a guy that often passively encourages violence on his own social media accounts, so take whatever he says with a grain of salt.
TLDR: We shouldn't be kicking people out of public universities because something they said hurt someone else's feelings, no matter how stupid the comment may be.