The decision to put you back on the street should be based on the threat you pose regardless of the reason you are a threat.

Certainly that's the way security states and dictatorships are run, but not states that have protections against personal liberties. If you have been accused or convicted of a crime of violence, you can't be put in prison on a 'preventative' basis just because a bureaucrat thinks you might be a threat.

This man might have severe mental health issues - but until he goes on trial for his crimes, he can't be imprisoned (subject to exceptions not relevant here).

Innocent regular citizens deserve protection and should have their rights respected to a higher degree than the career criminal or dangerous nutjob.

"Dangerous nutjobs" are innocent regular citizens unless and until there is a trial that determines they're not. That's the point - we don't give the government the unfettered ability to decide who is innocent and who is not except if they have a trial. This man appears not to have been convicted of any crime at all yet - at least, the article only mentions earlier arrests, not convictions. He is an innocent, regular citizen in the eyes of the law until he has had his day in court.