There is a perception that black individuals are being shot without reason. While I am not convinced there is a systemic problem I have seen numerous videos where black men are shot to death and clearly should not have been. That is what the protest and the BLM movement are addressing. 

Regardless of color, lipping off to a cop, refusing to cooperate, being pulled over should not be "rolling the dice". If a police officer does something offensive I should not be shot to death for saying so. 

In the cases above, some the people killed were in complete compliance with the law and the demands of the officer and were still shot dead. NONE of them (in the videos I saw) were in any way threatening the life of the cop or anyone else.