So-called Black Lives Matter costs black lives by making policing less effective. The "Ferguson Effect" has been documented. Recent headline: "104 shot, 14 fatally, over Father’s Day weekend in Chicago" https://chicago.suntimes.com/crime/2020/6/20/21297470/chicag... .
Police brutality and systemic racism caused a group to rise up and demand justice. The populace took notice, a movement was formed (BLM) and overall trust in law enforcement was lowered. Crime rose as a result.
It's not "so called" Black Lives Matter, it's "so called" equal and just law enforcement that caused the The "Ferguson Effect"