So, why the peaceful protests up till now, yet violent at the Inauguration and now on the Berkeley campus? The most obvious answer is to roll one's eyes and say, "Well, that's the Bay Area for you." Oakland and Berkeley are always having riots about something. (Seattle is no slouch, either). But the Women's March in the Bay Area went off without a trace of violence or disturbance.
Another answer may be that the Women's March was a daytime event, while the riots happened by night. And the anonymity of darkness does seem to attract violent protesters. But the Inauguration Day riots were well underway in the daylight.
Another possible answer might be that people fighting for openness and inclusion are not prone to rioting and violence. The problem with that self-serving narrative is that the anarchist thugs really do see themselves in those terms and define themselves as "anti-fascists." Nice way of showing it, guys!
Another answer, and one I was inclined to start out with, was that Women's Marches didn't have an actual enemy on hand to fight, and so lacked appeal to people going out looking for trouble. The Inauguration (obviously) had plenty of Trump supporters on hand to tangle with, and the Berkeley Riots had Yiannopoulos. But there have been pro-Trump rallies going on, not large, but also undisturbed (so far). And I note the article on the Women's March in the Bay Area mentions that the march encountered a right-to-life march, without tension.
So I am inclined to a slight variation on the theme. The rioters seem to show up when there is not just something to protest, and not just an enemy present, but an enemy they actively want to shut down, even though engaged in a clearly lawful activity.
The several times riots broke out among anti-Trump protesters on the campaign trail occurred when the rioters were actively trying to stop a Trump event and prevent peaceful and lawful supporters from attending a perfectly lawful rally.
The demonstrations that degenerated into riots following the the election were attempts to overturn a lawful election result.
The Inauguration Day Riots included attempts to block entrances and keep lawful supporters from attending.
And the Berkeley Riots were clear attempts to shut down Yiannopoulos' lawful, though odious, speech.
I can only assume that occasional pro-Trump demonstrators or right-to-lifers are simply not seen as a danger in the same sense.
Obviously the rioters and anarchists have no concept of free speech or freedom of assembly that must be extended to even the most hateful people. Our side cannot forget this distinction, and must keep reminding people of it as often as necessary. Up till now, the anti-Trump demonstrators have not had to deal with counter-demonstrators. That can't remain the case indefinitely. Sooner or later the counter-demonstrators will show up. When that happens, we have to be ready to keep things peaceful. Fortunately, the police are getting good at keeping hostile sides apart. Unfortunately, they are not infallible.
Other pieces of advice to our side to avoid trouble. Do not schedule protests around people or events that some trouble makers might want to shut down. Schedule them the day before, or a safe distance away. It may cut down on the people we might want to shut down seeing us, but so what? There will be plenty of other times and places to be seen without attracting the thugs. No night time events. Daylight is no sure protection, but it helps. No masks. We aren't afraid to show our faces. No clubs, crowbars, or other such weapons. And no blocking or shutting down lawful events. That way lies the end of freedom.