Thus, I think the only constitutional and fair way to apply such prohibitions would be that they are connected to a conviction for a crime and an associated professional diagnosis of such mental illness.

Otherwise it's just too "big brother", and sure, people aren't going to be as likely to seek help.

Bad idea.

For example, you have to sign away confidentiality in order for your insurance to cover a given treatment.

HIPAA is a rather bizarre magic act. While making a big show of protecting your information at one level (lots of rules about how providers must secure & transmit records etc.), it reduces the restrictions on how insurance companies can collect and use that same information. Believe me, I've sat through many hours of training on these topics.

I'm scared to death of the things. I have a "diagnosis", depression and anxiety. My big worry is with people's personal medical records possibly being linked to other databases, or with people being able to get their hands on them for reasons other than medical care.

I don't know what the answer is, as least one that the public could accept. But I hope things aren't done that make it risky for people to seek help for mental illness, that would be going in the opposite direction from where we need to go.

Depressed people just bring others down, anyway.

individuals from certain rights by, for example, committing them or protectively placing them in certain designated facilities. The difference is that we do this on an individual, case-by-case basis, with each person being subjected to a detailed individual examination and court proceeding, and only committed or placed if the court finds them to pose a danger to themselves or others, or finds that they are unable to reasonably care for themselves.

Anyone with a contagious decease needs to have their rights restricted.
How dare anyone get depressed in polite society? It brings other people down!

While that might not be a good idea from a severely depressed person's POV, his family will appreciate it.

Barring gun ownership to paranoid schizophrenics is an even better idea. While few of them are violent, the ones who are do a hell of a lot of damage, especially when they're allowed guns.

However, the psychiatrist should be the one to determine whether people with the milder personality or affective disorders should be allowed guns. Yes, they'll make an occasional mistake, but it's better than having a rigid policy in place that doesn't account for individual differences or an opposite policy that gives every felon and lunatic the right to a firearm.