This is probably one part of it, but I'm not sure it's a very big part. Sacrificing yourself for the group is still a part of some east asian cultures but they aren't doing any better in this regard.
I think we've always been this way, but before easily available birth control the need to have sex has been enough to keep the birth rate high. Now that sex no longer has to lead to reproduction, humanity will have to evolve some other way to increase birth rates. We will start seeing cultural and/or biological evolution; cultures and personalities that have more kids even when birth control is available will survive, and the rest will die off. Future humans might have a weaker physical desire for sex, but a stronger psychological desire for offspring.
I think we've always been this way, but before easily available birth control the need to have sex has been enough to keep the birth rate high. Now that sex no longer has to lead to reproduction, humanity will have to evolve some other way to increase birth rates. We will start seeing cultural and/or biological evolution; cultures and personalities that have more kids even when birth control is available will survive, and the rest will die off. Future humans might have a weaker physical desire for sex, but a stronger psychological desire for offspring.