However, the altruism which group selection can create is quite limited. Altruistic behaviours can only evolve by group selection to the extent that between-group selection results in direct fitness benefits to the actor's genes - i.e. fitness benefits to the actor or their relatives.
That's quite a tall order. By contrast, the memetic explanation of altruism invokes brains being hijacked by cultural symbionts, which manipulate their hosts into behaviours that help to propagate themselves. In particular, they stimulate social behaviour that prmotes contact between their hosts.
The effect on the host's genes matters very little. The host can be sterilised, and the mechanism still works. In fact, the fewer resources the host expends on producing genetic offspring, the more resources are available for producing memetic offspring.
Memes can thus produce extreme altruism. They can produce pathological altruism. We can see - by looking at hunter gatherers - how much cooperation and altruism comes from having a hefty dose of memes. I don't mean to belittle other mechanisms too much - but human altruism towards non-kin is - overwhelmingly - the product of memes.