I don't know if I can explain it adequately.
Throughout history, segments of society that have been repressed or minimized have erupted violently and loudly when they see a chance to truly change things.
I'm sure it happened earlier, but the first incident that comes to mind is the slave rebellion against Rome led by Spartacus almost 2100 years ago - 71 BC.
That was a lot bloodier than graffiti in public places and it was not a racial movement. Slaves then were often captives taken after one of Rome's many many battles to take new lands.
The lesson we need to learn is that revolts don't stop permanently until change takes place permanently. It's a lesson we (whoever the suppressing class is) ignore at our peril.
BLM is meant to keep "you are doing wrong and you are allowing wrong to be done" ringing in our heads.
Another translation could be "every symbol of your comfort and complacency" is a target, until we too are consistently invited to every privilege and opportunity.
It seems a fair idea to me.