To be clear, this is nazi shit and is in and of itself revelatory of some alarming preconceptions and attitudes you hold towards the mentally unwell. I know others in this thread have said the same, but if I'm gonna reply it'd be remiss of me not to bring it up.
But it's also just a really fucking stupid idea…? Like, on a practical level, where are you finding all these professionals to assess the entire population? How do you ensure their assessments aren't affected by their own personal or institutional biases? How do you intend to partition "most people" (your words) from society without causing said society to collapse due to the sudden removal of a majority of its constituents??? Where are you keeping your undesirables, how are you looking after them, and how are you maintaining the necessary supply chains to sustain not only what's left of broader society but also at the same time the institutionalisation of "most people"??? And c'mon, be real, most people don't want to get locked up, so what's stopping them from just lying to their counsellor during their assessments? I know I would, and I consider myself to be far more mentally healthy than the typical user on here.
Not only are you an evil human with a contempt for the wants and needs of your fellows, you're also a fucking imbecile if you genuinely believe this is in any way workable.