It doesn't depend on altruism, if everyone does it it just results in assortative mixing and you wind up hanging out with people who can stand you, if any. It

It doesn't depend on altruism, if everyone does it it just results in assortative mixing and you wind up hanging out with people who can stand you, if any. It also avoids the common human-behavior anti-pattern where two people remain in a mutually self destructive relationship because each is under the delusion that the other can't live without them.