I read about evolution, animal behavior (humans are animals), and game theory. I tend to look at evolution from Dawkins' perspective, which is based on gene survival and includes individual actions, social actions, and the physical characteristics of the "meat machines" used for transporting and copying genes. There is a genetic basis for animal behavior and anyone who denies that doesn't know much about evolution. For example, many animals risk their own survival to warn others in their group of a predator. That isn't "social Darwinism" or "altruism", it's gene survival - because when virtually the entire population has this trait, the genes (individuals) in it tend to survive better than the population that doesn't have this trait. This natural selection extends to many, many kinds of behavior, including the social pressures we've talked about here. Again, it isn't "social Darwinism", altruism, or any of a number of other misnomers for this kind of behavior. It's simply natural selection at work.
And just an FYI - one of my sisters has never been married or had children and is well over 60 at this point. I have no problem with her life choices at all and never have had. I guess the next time we talk I'll have to broach this subject with her. We've never talked about it because, quite frankly, it's none of my business how anyone's lives their life as long as it's not overtly harmful to me.
Obviously humans are animals, and our instincts control our behavior as a matter of simple default. I might even accept that this is the level the majority of people operate at the majority of the time.
But you can't simply ignore the other things our high intellects compel us to do. You can't compare us apples-to-apples with any other animal, because none come close to our brain structure. The closest is probably dolphins, and if you take a good look at them, you'll see they display some of the same evolutionarily meaningless behavior that we do, although not to the same extent.
Humans -- some of them, anyway -- spend a great deal of their time doing things that have nothing to do with tribe survival altruism, reproduction, or self-preservation. Why do we make art? Why do we learn about the distant cosmos when, at least at first blush, we have no reason to believe this has any affect on us? Why do we do things for the sake of mental intrigue that are overtly risky to our lives, and don't offer any survival benefit to our "tribe"?
Because we're just not that simple. You can't think of humans as though we just go into heat.
We've got mental energy to burn, and we burn it in all kinds of ways that offer us nothing on the level of the selfish gene. Hell, half the point of trying to make life so easy for ourselves is to give us more time to do these evolutionarily meaningless things.
And I might also note that Dawkins knows nothing about sociology. It is not his field of expertise, and he is not qualified to speak about it. He is also exceptionally poor at philosophy, and listening to him debate the religious on that level is embarrassing to me -- and I'm an atheist who agrees with him.
Just because Dawkins is famous and is qualified in the field he
actually knows something about (biology) does not make him an authority on all things. He is extremely ignorant about a great many subjects, regardless of how much he talks about them.
But even ignoring all that, if you want to think of humans in such a simplistic way, the childfree serve a very clear purpose for the same reason altruism does. We spend much more of our lives working, and often working in very challenging and humanitarian fields. And if your argument were true, we would be appreciated by society for the same reason altruism is. The purpose we serve "the tribe" is quite obvious, even if it doesn't benefit our own genes.
And yet, we are not. And we are especially maligned in societies that still suffer a lot of sexual repression and misogyny. Gee, what a coincidence.