To be fair, I don't think they did. Nothing they wrote precludes polyamory and lots of sex, I think what they say is if you are gonna get sex, better try to be

To be fair, I don't think they did. Nothing they wrote precludes polyamory and lots of sex, I think what they say is if you are gonna get sex, better try to be really good at it. I think bigger problem with their perspective is that it is very egotistic. For example, the pleasure of playing a video-game really well (a long-term goal) is more important than a pleasure of spending an ad hoc evening with a loved one (a short-term one). I suspect most humans have evolved to not only be happy about reciprocal altruism, but to give unconditionally. Because if you are just happy with reciprocity, then the resulting equilibrium can be cooperation or lack of it, both are possible. If we are (as social creatures) rewarded for both reciprocity and giving unconditionally (or perhaps, seeing reciprocity realized for others), the equilibrium is more cooperative.