So from what I understand, rule utilitarianism as a doctrine states that in order to maximize utility, we should evaluate actions based on rules that, if we accept them, would maximize utility in the long-run. The typical rationale for this, as I understand it, is that if we were in a society that felt that people could violate people's basic rights whenever they feel it maximizes overall benefit, no one would feel secure and everyone would be less happy in the long run. But does this apply for every case?
Say for example three people are in a boat, all starving, and 2 of them cannibalizes the other. No one ever finds out, it doesn't affect society at all, and two people don't starve to death. How would the rule utilitarian justify this action being morally wrong?
Thanks for any responses you provide.