I don't like the framing of the behavior as somehow irrational or random or clinically-diagnosible. It's not irrational to get involved more in a movement when it is a movement, and seems like it might be gaining traction. Just like it's not irrational to not-boycott some useful, cheap product even if you strongly disagree with some of the practices that go into its production, but to join a boycott if it starts and seems to be gaining traction. In fact, it's less rational and more tied up with self-image than with utility to do the former—and even so it doesn't mean that people who do things like solo-boycotts are wrong, or bad, or misguided, at all.
[EDIT] to put it another way, there's a cost to political action. That a lot of people might see that cost WRT anti-police-brutality protests as lower, and the benefit it yields higher, this week than they did two weeks ago, and so be willing to participate, is not "emotional hysteria". Not that nothing that could be described as that has been involved at any point in the process, but that seems reductionist to the point of being very wrong as a characterization for the overall movement.
Objectively speaking becoming involved in a trend only for the sake of a given trend becoming more trendy strikes me as directly irrational. It’s following for the sake of following only because that’s what followers do which is circular and absent of any original consideration.
But humans are social creatures, beholden to social norms. Doing something just because other people do it is literally how society works. There are very, very few (if any) "well-adjusted" members of society who don't do many things just because that's how other people do it (a.k.a. it's "trendy"). If you behave otherwise, you're likely be socially outcasted.
Of course, if you're saying society at large is irrational I pretty much agree... but within the context of social expectation, I'd say it's pretty rational to compute that your contribution is more likely to land once a movement has already started. If anything, those who first begin the movement are the most irrational (since the likelihood of success is much lower compared to the personal cost to the individual).
In other words: if you live in an irrational system, the only way to be rational is to behave irrationally.
There is nothing objective about your comments. That's just another veneer of credibility.
Same with calling protestors "irrational" -- maybe to your point of view, they are but this is not an objective statement by any definition of the word.
[EDIT] to put it another way, there's a cost to political action. That a lot of people might see that cost WRT anti-police-brutality protests as lower, and the benefit it yields higher, this week than they did two weeks ago, and so be willing to participate, is not "emotional hysteria". Not that nothing that could be described as that has been involved at any point in the process, but that seems reductionist to the point of being very wrong as a characterization for the overall movement.