1. As far as I know, kin selection is a subset of group selection, they are not mutually exclusive.

2. I don’t talk about either specifically. It’s a general observation. If resources are limited, it can mean that reducing the number of consumers can improve outcomes for remaining people.

3. Do you mean human genes or genes in those microorganisms from the other commenter?

Kin selection is specifically about shared genes in the kinship group. Group selection can include woolly thinking about 'benefit to the species' when it's simple not possible to increase the frequency of a gene in the population if it's only in the sub-population that dies.

It's interesting when thinking why there might be evolutionary reason for suicide, it could be for benefit of the group, however in modern life people like to tout that it's a selfish act. Things have changed in modern life of course.

Possible leftover maladaptive behavior. Or maybe it is still adaptive (for the group) in whatever indirect way.

Sacrifices in the old days are speculated to be healing for society by venting certain violent impulses out. Perhaps suicide could be healing by having society take a look at itself and reconsider something, but in modern days this would not work as they are not publicised.

I am intentionally adopting an extremely society-centric position, to counter-balance individual-centric position usually adopted by default. (Again, an individual literally does not exist without the society.)

I think that's fair to look at it societally, but the concept of a collective goes up and down fractally. You have self, family, neighborhood, town, etc going up... and then going down you have organs, commensurable organisms, cells, genes, etc. All replicable and self interested in their own contexts.

While we can argue against overgeneralizing, models from one scale often elegantly explain dynamics in other scales. Apoptosis, auto-immunity, depression (learned helplessness) can emerge at scales other than where they are most familiar.