As far as the particular wording of 'psychologically unstable,' perhaps a more precise phrase could be found to replace it, but I don't think the mental health issue should be edited out entirely against the question author's wishes. This seems to explicitly violate SE's policy of not changing the author's intent in edits and is a rather substantial change to the meaning of the question. Some of the title edits significantly broadened the question to the point where it would have included things like terrorism, for example. That essentially makes it an entirely different question from what the author was asking about.
Regarding changing the meaning of a post, the help center page on editing states that edits can be used:
To clarify the meaning of a post (without changing that meaning)
(emphasis is theirs)
As far as the question itself, it's not speculating about anything and does not seem to violate Aviation SE's on-topic policy with regards to not speculating about recent events. Asking a question that occurred to you because of a recent event isn't the same as speculating about what happened in that particular event. The question also has several good answers (including a rather highly-upvoted one) that answer the question without any speculation at all about the recent incident.
What our on-topic policy says about recent incidents is listing this as explicitly off-topic:
"What happened to Flight 12345?" when the incident is still under investigation
Note that it is the speculation about recent incidents (or inviting such speculation,) not the mere mention of the incidents, that makes a question off-topic. Given that the answers aren't speculating about the incident (or even mentioning it in most cases,) I'd say this question did a reasonable job of not inviting such speculation.
Frankly, most of the comments on that question seem to stem from the edit war on the question rather than the content of the question itself and probably should have taken place here in meta or in chat. So, thanks for asking here. :)