Calling someone a sad excuse of a human being sure sounds like an assessment of their mental state lol.

This is a forum. People will say stuff. You may or may not agree with the stuff they say. They'll do it anyway. Judging someone's mental state as an outsider is fine as long as you don't purport to do it from the perspective of telling them what to do next, that's pretending you're a doctor. But I've seen plenty of actual doctors do remote diagnosis of Musk's various mental issues (ditto: Trump, Putin) and I'm fine with it, I just take it with a grain of salt. If we take being a sad excuse of a human being as a reflection of someone's mental state then you are in fact engaging in the same, the only difference is whether or not you use terms with clinical relevance.

What’s the difference between an outsider and, e.g., his therapist? Consent? Proximity?

Curious; not trying to bust your balls.