>He's wrong for a simple reason: Breasts are expensive. They are expensive to maintain, and no other animal maintains them.
Your argument is not valid. It's not the cost alone that count, but the benefits minus the costs. Imagine your argument against human intelligence instead: Human intelligence could not have evolved for a simple reason: brains that produce intelligent behaviour are expensive. They are expensive to maintain, and no other animal maintains them.
I just read through the group selection wikipedia article. It does not seem to be abandoned as a theory, it seems to be a topic with proponents on both sides, and there are strong arguments for both sides. The selfish gene argument is an old one, and it's just mainstream, that's all.
Your argument is not valid. It's not the cost alone that count, but the benefits minus the costs. Imagine your argument against human intelligence instead: Human intelligence could not have evolved for a simple reason: brains that produce intelligent behaviour are expensive. They are expensive to maintain, and no other animal maintains them.
Also: please read up on the unit of selection http://en.wikipedia.org/wiki/Unit_of_selection. Selection on the level of groups (let alone "society") is very, very unlikely (to say the least) and has long been abonded as theory http://en.wikipedia.org/wiki/Group_selection.