So seeking confrontation is the problem from both sides. Some people want to protest, some want to confront. And the police prepare for worst case ... which means confrontation which escalates...
Then you have opportunists who just want a fight .
Domestic abusers (not always people prone to violence) are sent to classes and often get in the same situation again, even after training and knowing the legal consequences.
Sure, it's hard to overcome instincts, but it's far from impossible, and most of the police that have been actively creating these problems haven't even started trying.