Not going to try to defend the actions police or anything (I think the protest is for a good cause), but one piece of info I think is valuable:
Mob mentality is dangerous. There is a thin line between a "peaceful protest" and a riot. If you have seen other protests that have turned into riots (like in France where several innocent shops got destroyed in an anti-Israel protest), or in England where the riots got way out of control, you know what can happen. Its a few police trying to keep a huge crowd in control - and it is a scary job. Unfortunately being well-armed makes the crowds even angrier.
Mob mentality is dangerous. There is a thin line between a "peaceful protest" and a riot. If you have seen other protests that have turned into riots (like in France where several innocent shops got destroyed in an anti-Israel protest), or in England where the riots got way out of control, you know what can happen. Its a few police trying to keep a huge crowd in control - and it is a scary job. Unfortunately being well-armed makes the crowds even angrier.