I don't really think it's fair to see all Trump supporters as people who would do this. I definitely think it's a bad idea to just get rid of the chalk, because that doesn't make the supporters go away. It just makes them feel wronged and if anything more supportive.
No definitely not all trump supporters are like this. But there are enough to be scared of (see the poll results in another comment of mine in this post). Like with Muslims, I think go after the preacher that's radicalizing them.
None of what you quoted from those polls asked Trump supporters if they were in favor of actually going out and killing minorities. Or even threatening to kill. I live among plenty of dumb rednecks with bullshit views, but I've only ever had to report one whom I can only hope is being monitored. Even that guy would never have the guts to do anything, they are all incredibly weak people. Still have to report him though because ya can't really play around with that. The thing is these people were around before somebody wrote Trump in chalk. They were around before Trump even started running for the nomination. What these students are upset about is their false sense of security being lifted. So for people who had that feeling lifted long ago or for people who never had the luxury of having a false sense of security it does seem silly to get upset at chalk drawings.