Think about this for a while.

Who makes the diagnosis? What happens if the diagnosis is wrong?

When is someone declared "cured"? Ever?

What if people avoid treatment, and thus identification, to avoid having basic human prerogatives taken away? Will we have the medication police?

Shall addiction of any kind be included in the restrictive class of ailments? What happens to all the internet addicts out there, the people who are glued to the TV, the workaholics, those of us who drink too much coffee? Do they count, or will this be confined to those whose vices are illegal or disgusting to a large enough segment of the population?

How about the chronically, unrealistically happy? Are they to be classified as mentally ill in spite of the fact that they cause society no trouble? Is causing society trouble the benchmark for "mental illness"? If so, will inconvenient or difficult people be "diagnosed" in order to restrict their participation in life?

Suppose a mental illness is shown to be heritable, but doesn't present in all carriers. Are the carriers to be identified to prevent them from reproducing, so as to avoid future costs to society?

Now, substitute "cancer" or "diabetes" for "mental illness". Bad idea then, yes? Still a bad idea when it's mental illness. It's precisely this kind of thing -- placing the mentally ill in the same general category, "undesireables", with criminals -- that makes people reluctant to be marked by seeking treatment.