If this was the only time BLM did something like this you'd have a point. But it happens a lot. The argument that "it's a big organization with sh**tty or nonexistent leadership with a bunch of random loud moths regularly embarrassing them but the general purpose and overall goals of the group is a net good for society" is a much better angle than the one you seem to be taking.
I just don't see why anyone would make a big deal out of this except to discredit the broader message of BLM.
It's part of a broader issue with the messaging of BLM, and the control that extremist elements exercise over it. This is hardly the first time that someone affiliated with BLM has done or said something that is, at best, counterproductive. Considering the influence of those extremist elements, there is a serious question to ask: is the organization in question an effective means by which the message we are describing can be advocated?
