I think most people find it easier to believe in group selection for altruism in the evolution of culture than in the evolution of organisms. For one thing, people think about culture and can change the rules, so that complex adaptations, like punishing free-riders, can appear quickly.

ETA: the evolution of multicellularity seems like a good candidate for group selection to me. Once it has been achieved, few would call it altruism or a group, but the intermediate stages probably require group selection.
I'm putting this on the comment about culture because multicellularity involves commitment mechanisms, which are like ways of punishing free-riders.