Who's "they"? Your issue here is you're taking this amorphous movement that currently doesn't have any leaders and judging it by the actions of a few. Essentially you're saying no one derserves to be heard because a few folks broke some windows and brandished knives. You're saying that the police should continue to murder unarmed poc with impunity because some rioted as a consequence of it and we can't have that.
The problem here is that the actions of a radical few will infect and spoil the intentions of the honest majority, as it often does.
No honest person condones what these police forces do, but many will fail to realise what the movement is about when innocents are attacked/murdered/etc.
Not that that is smart either, but hell you can't argue that this behaviour helps the cause in any way. Come on now, you know what people are like. A person is smart, people are stupid and easily scared etc