I don't loving care what the race of the kid or the attackers is or who they support, if you beat up a mentally disabled kid for any reason you are irredeemable scum who needs to learn what it's like to have endless pain doled out on you. That's the only way you'll ever truly learn.
That being said, let's not pretend that this is new behavior for BLM supporters. They've been doing things like this for a while now, and it's high time they took responsibility for all of it.