“What else is needed?”
An actual crime.
I guess some of this might dance on the edge of being a “threat,” but to be legally actionable a threat has to be very specific — not “I want to kill someone,” but rather “I am going to kill John Doe.”
And proving someone is crazy enough to deprive them of liberty (being a threat to himself or others) is very hard thanks to the liberal supreme court of the 1970s and .. . . believe it or not . . Geraldo Rivera who made his name by producing slanted and salacious shows on mental institutions, which turned public opinion against locking up crazies.
A mental commitment is not a jailing