You’re right, those who are cops did have a choice when they chose to become officers. And knowing the danger they would be in, still signed up so that they could protect you and me from those who would want to harm the innocent.
They signed up to fight criminals and bring those who break the law to justice. They didn’t sign up to be targeted by the people they swore to defend because there are some bad apples in the bunch.
MLK, probably one of if not the greatest Civil Rights Activist in American history, would condemn the tragic killings of George Floyd and the other PoC who were murdered, just as much as he would condemn the violent rioting and burnings that have destroyed the livelihoods of so many innocent people, and just as much as he would condemn those who target and kill police officers simply because of the badge they wear.