I find it hard to believe that a tendency to rape (or more specifically, the psychological traits that make one more likely to be a rapist today) wouldn't have been a fitness advantage in at least some of our forager ancestors. There are too many examples in societies close to our own where various forms of rape or were forgivable/forgiven (by society, not necessarily by the victim): rape of foreigners in war, marital rape, rape as punishment, protection of the rapist by an influent member of his family, marrying the rapist ... sure, some of those situations may not happen in a forager society, but there may be different ones that do happen.

Having a reputation as a rapist makes it harder for him to survive

This supposes that the society in question has a concept of "rapist" analogous to our own; I suspect many societies would have different concepts, and only harshly punish some of the behaviors (rape of enemies and marital rape seem to usually get off the hook, except in very recent history).

As an illustration of the way different societies approach the problem, I've already been in a conversation with African men who were saying how under certain conditions rape was an acceptable way of getting sex from a girl.

That being said, I don't know much about how foragers approach the question of rape, I'm merely skeptical of the idea that they have very few children of rape.