That may be in the case in some situations, but I can recall several major, i.e. large, protests that resulted in very few arrests or problems with the police.

That may be in the case in some situations, but I can recall several major, i.e. large, protests that resulted in very few arrests or problems with the police. In fact, some of them were a quite pleasant crowd if the reports were to be believed. Sadly, you just generally don't hear much of them in the news.