One practical problem is that there are a fair amount of people who are simply unstable, and if told why they were rejected (in very neutral to positive framing) they will actively challenge it and even go pseudo-stalker mode over it.

Dealing with just a handful of these guys is enough to do away with providing any sort of feedback. Like many things, a few bad apples ruin nice things for everybody.

> One practical problem is that there are a fair amount of people who are simply unstable, and if told why they were rejected (in very neutral to positive framing) they will actively challenge it and even go pseudo-stalker mode over it.

What kind of positions are you hiring for that you've encountered this? It sounds so absurd that I would guess you're describing a twitter/reddit troll without the context, not a professional position.

ghosting in no way solves this problem, it's universally acknowledged as worse than a simple 'no'

Then we have a right (and moral right) to ghost companies without any notice, too.

Yes, in the US you do. Makes you look bad just like it makes a company that does it look bad.

Isan email that says we've moved on with another candidate sufficient or do you have to give the exact reason?