BLM is the worst movement conceivable.
Take a pretty universally reviled problem, police brutality. Now let's ruin that.
Start off with a divisive title that immediately splits the room over semantics. Good start.
Now to rally around an event. Police killing someone isn't that uncommon so pick one. Oh, how about a case where the police was in the right to kill them. If/when it goes to court it'll only reinforce the idea that the justice system is racist. Just will have to ignore the evidence and alienate some more people. Very nice.
Time for some protests but what if they actually just facilitated arson and looting. Don't worry, property can be replaced so long as its not yours. The police will help you by chasing you around the city instead of stopping the looters ruining an otherwise peaceful protest.
After some spicy protests, let's demand some reform. Fuck it. Let's demand sheer police abolition. We'll have some infiltrators parrot "abolish the police" until it picks up steam.
Finally, after you've wasted all your good will, slink back into irrelevancy and ignore the actual police brutality because everyone hates your guts.