I was primarily responding to your suggestion that strict social rules around sex were an intrinsically Christian take (or religious in nature).
Beyond that though, Chimps have social hierarchies around sex. It’s hard to imagine why something you believe to be so counterproductive would exist so persistently across cultures and times unless it had serious value.
I don't even necessarily believe it's counterproductive, it just seems intuitively expected that closing off a topic for broader discussion is a way to breed unhealthy attitudes and abusive behaviours involving sex. But doing so seems to have benefited some people I suppose. Or maybe it really is due to an innate desire to maintain an aura of mystery around it. I don't think anyone really knows.
Beyond that though, Chimps have social hierarchies around sex. It’s hard to imagine why something you believe to be so counterproductive would exist so persistently across cultures and times unless it had serious value.