[sonofhans]

I do not believe there's evidence or reason to say that suicidal tendencies convey evolutionary advantage to the species. Many things seem to be accidents. Does the https://en.wikipedia.org/wiki/Photic_sneeze_reflex convey advantage? Very likely no; it's an accidental mutation that doesn't cause enough damage to be selected against.

Evolution isn't directed, and there is no end state. Attributing positive effect to every mutation verges on https://en.wikipedia.org/wiki/Teleology.

[snagglegaggle]

What would convince you? It should be pretty clear at this juncture I don't have evidence. However I did give a reason; if in general depressed people feel they are not contributing or participating in society then that is pretty clear.

You can look into this further: a lack of physical activity tends to worsen depression, and a hunter-gatherer with reduced mobility and/or other issues that make it hard to interact with the group is most certainly a resource drain. It goes on and on.

Evolution isn't directed but structures and instinct that are truly against the organisms interest are the exception, not the norm.