What profession has an effective method of weeding out abusive people?

This is 100% a bad faith question. And even if it's being asked in good faith, it's entirely irrelevant. It's essentially whataboutism. But I'll address it anyways.

If I have an abusive co-worker in my tech job and my manager and HR refuse to do anything about it, it just makes work suck.

But an abusive cop ruins lives with bullshit charges and bullshit handling of innocent people. In worst-case scenarios, they're murderers that get away with it.

So yeah...it's a pretty clear distinction, and I refuse to believe you're asking this question in good faith.

It's not in bad faith, but it is rhetorical: people protecting their own, at an industry or occupational level, is the rule, not the exception.

Yeah, the problem is, as I mentioned, the consequences to society are very different between a cop being abusive versus your local plumber or other $JOB.

For violence? Really? When was the last time you found yourself defending a coworker who beat someone up in the workplace?

It's not whataboutism, it raises a good point: What's the best we can do with regard to weeding out bad cops? Like, what does doing a good job of that even look like?

The ideal is obviously 'no bad cops' but everyone here can agree that's not really achievable, so what does doing a reasonable, or even great job look like. How many bad cops are on the force if we do everything we can?