When I was in university, the elected student council were childish and stupid. I thought maybe the world was doomed if these types are our future leaders, or maybe a lot of young people are just immature. I think I was right on both accounts.
BLM was set up by student political activist types. I don't expect all of them to be able to run an organization well, or have the most maturity. It doesn't mean black lives don't matter, I guess it also means that power corrupts, which is ironic and might make them better understand cops who behave like jerks.