Counter point, the road to hell is paved with good intentions.
I'm not gonna argue your brother ("my sister in law is the wife of a cop" is a strange way to say that) is evil simply for being a cop, no, but your brother does defend bad cops all the time. Every cop does. They call it a brotherhood for a reason, and the expectation is that their brotherhood runs deeper than yours. Be aware of that and keep him aware too. Because if he's "one of the good ones" he's in real danger if ever he spoke out against the bad ones. Real, life threatening danger. That I can say that of police and back it up with a dozen examples of cops killing other cops should at the very least give you pause.
By the way if you do the "don't assume their gender" thing from my assumption that it's your brother, oh boy they're in a lot more danger than I originally thought.