Now I see how you are reading the “kind of claim that a utilitarian could make” bit.
As you previously observed, the actual answer to this involves cultural evolution—not group selection.
The “evolutionary psychology” explanation is that humans developed sophisticated culture which was—on average—beneficial, but which allowed all kinds of deleterious memes in with the beneficial ones.
A utilitarian could claim:
Evolution has produced in me the tendency to value the welfare of non-kin at a significant fraction of the value of my own personal welfare.
...on the grounds that their evolution involved gene-meme coevolution—and that inevitably involves a certain amount of memetic hijacking by deleterious memes—such as utilitarianism.
Now I see how you are reading the “kind of claim that a utilitarian could make” bit.
As you previously observed, the actual answer to this involves cultural evolution—not group selection.
The “evolutionary psychology” explanation is that humans developed sophisticated culture which was—on average—beneficial, but which allowed all kinds of deleterious memes in with the beneficial ones.
A utilitarian could claim:
...on the grounds that their evolution involved gene-meme coevolution—and that inevitably involves a certain amount of memetic hijacking by deleterious memes—such as utilitarianism.