True. It's a mess.

Pedantically that doesn't take away from your point but asserting just for clarity because I see people bring it up a lot:

The infamous Killology lecture isn't taught to the vast majority of law enforcement in the US as I understand it. We certainly didn't receive it (or similar) at my academy.

I've heard it isn't quite as bad as cherry-picked-and-taken-out-of-context-to-malign, but I've personally never watched it, much like I haven't read Mein Kampf; "That seems like a soup sandwich of nasty, so I'm not going to waste my time."

As previously mentioned, they simply bottle it up. It's not hard to "I've never had any suicidal ideations" your way out of any mandatory screening as currently implemented. Some are better at rooting out deception like that, but apparently that's not in the budget. I received an MMPI-style questionnaire and subsequent interview, but so did all three of those peers I mentioned who passed just the same as I did. Hell, one of my academy classmates told the psychologist he thought he was Batman. When pressed for why, he relented and said it was an outburst because he was distraught due to his goldfish dying. He obviously made it through with a Pass and I think is still on the force many years later? His social media is intentionally obscure so it's hard to say.

Truth be told, reforming law enforcement in this and other ways is simply not politically motivating for most Americans; they're generally either focused on other single issues, "The police are perfect and criticizing them is immoral," or "The police are all bastards and need to be abolished."

I'm not dumb enough to tell everyone I meet I was a cop so all of my discussions about the matter are generally relegated to the internet, but of the people I bump elbows with on the topic on Reddit, 90% of the time it turns into name-calling and other bad faith tactics. The other evidence I use is... -gestures broadly at the state of US politics-. Remember when people were marching in the streets to fix the police? Remember how it generally didn't?