Quick solution. Anyone arrested for vandalism or violence during a protest turned riot....IMMEDIATELY loses any Federal or State aid they are receiving (if they are). To get it back, they must go through a program educating them on proper protest, and prove to a judge they will change their ways. On any second offense of this, that aid should be revoked permanently.
Once the word is out about the penalty...you'll see attendance at such nonsense plummet dramatically......
This is not to assume that ALL protestors are on state benefits...but they sure weren't busy at work either. So.....