I agree racism is bad, but why can’t black people be civil and polite when asking for equality?

The thing is that these people aren't being honest when they say things like that. They're lying, but they're often lying to themselves as much as to others. They always have some objection or another to opposing bigotry. Because the reason they're giving is just a post hoc justification for opposing progress.

Think back to the George Floyd protests. People said the exact same thing, that they oppose racism, but they can't abide riots (even though the overwhelming majority of the protests were not violent). Then later, an NFL player kneeled during the anthems, literally the tamest, most inoffensive protest I can imagine. And people lost their minds.

It doesn't matter how disruptive or civil the protest is, it will never be inoffensive enough, they will always oppose it. And if you somehow do find a form of "protest" so inoffensive that they accept it? Then they'll ignore you.