I've seen it too often now, in person and online, for it not to be the result of training. I've even read someone else online (I don't recall where) attesting to the phenomenon: as soon as demonstrators engage physically with police, counter-protesters or innocent bystanders, those not in the scrum start chanting "peaceful protest." Once when they were trying to invade a downtown hotel, blocked by a cordon of police in riot gear (I later learned from hotel employees that they were trying to get at someone with a Trump hat or sign inside--presumably to trump his hate, good and hard) they started in with it--the effect was a bit sinister, as if they were deliberately taunting the cops with irony.
I'm not sure if the idea is to settle down their overexcited fellows or an attempt to frame the event as it's happening (and being recorded from multiple angles) in their favor. It appears to be the latter. There's more and more organization behind the protests, and the protesters are picking up experience and habits.
The "special snowflake" theme has to go away. There are many among them now committed to violence--there have been no consequences and the precedent has been set, with the attack on Richard Spencer, then a counter-protester knocked unconscious here in Portland, and tonight's escalation. They are in a self-control spiral, as the more zealous compete to distinguish themselves against these increasingly violent examples. The safety of the mob and delusional zealotry gives courage to many.
The "special snowflakes" thing always only went so far. These demonstrations are expressions of power, and they are intoxicating. The dimmest among the mob, and these must be many, if not the majority, may in fact think they've been powerless and oppressed all this time (ironically as a result of all the coddling they've received), and their lashing out has the energy of released frustration.
That frustration may in fact be real, just displaced. They don't know what they've been denied--family, faith, community--by modernity, technology, atomization, indoctrination--so their frustration is displaced onto these same things, which they've been trained to think of as the problem.