I've often wondered if depression is exactly that, a system level optimization. Sometimes depression just happens, but sometimes it is triggered by low social status, realizing you've hurt someone in an unjustified or accidental way, having other mental illness, being seriously injured, or some other way that threatens the fitness of the overall group. Depression might be a (albeit flawed) system level way of reducing the amount of physical and social resources those people consume so that the non-depressed strata of society can better take them.

Note: this is a speculation, not assertions of fact

I think its just a natural consequence of our mind working on a positive-negative reward system, which I think its critical to any intelligence. Being manically positive is just as detrimental as being chronically depressed.

Its entirely normal to be negative, or to ignore stimuli, or decide not to do things. In some situations, say if you were trapped in a cage your whole life, you'd agree it'd be entirely normal to be depressed. It would make no sense to waste energy running around hitting iron bars that won't break.

In this sense, depression is somewhat of a social construct. We determine someone is depressed because we believe their reaction to the environment to not be normal.

You’re proposing group selection, which always never happens.

Evolution functions not at the level of groups, or even individuals, but genes inside of individuals.

Most of the time thinking of it as group selection at the genetic level (=individuals) does work, fortunately.

Such phenotypes would fail to reproduce, leading to the genes for those phenotypes dying out.