As I said, regardless how you feel about graffiti as an art or communications form...
Denzel McDonald was not running around being a "violent" "criminal" making "racist messages" - these are the words being used in the OP about him.
Moreover (contrary to the impression the OP is trying to give), the school faculty and students are not objecting to Denzel McDonald facing repercussions for his graffiti. Their objections are to the disproportionate manner in which Denzel was arrested in the classroom during class - an action that disrupted the class to the detriment of other uninvolved students. Two different officials of the school have already acknowledged that this action was wrong and have apologised for it.
Faculty is also calling for a stay of expulsion. As was noted above, their position is that "even the rash of violent crimes on campus such as rape and sexual assault have not received this kind of response".
I would also note that Denzel's graffiti is in response to truly racist graffiti:
The university has experienced several racist incidents in recent months, including students finding graffiti of a man hanging from a tree in a campus restroom.
Was a classroom disrupted and that vandal expelled?