We ban murder even though most homicides go unsolved...

Like, I don't think there's a single crime where 100% of the time they find and charge the culprit

Even suicides, sometimes that's insurance fraud and ruled an accident, a single time means it's not 100%.

The point of laws/rules isn't to always stop something. It's to make the law/rule clear so people know to abide by it, and people who don't can't plead ignorance.

I'm aware, that's why my comment mentions that

Yeah but that's self-reported, the user has to set it on themselves.

Nothing prevents bad faith bots from just not setting it

This is exactly the problem I mentioned, in that it's giving people a false sense of security. There are bots posting without that symbol all the time.