What's really ridiculous is the idea that if sex didn't feel good we would all die out. Sure, we would have less 14 year olds having babies. But adult comitted couples who wanted children would have sex to get pregnant once or twice, even if it was *painful*. I'm just so tired of hearing that silly argument.
Perhaps in the here now, since we have evolved to understand sex. How about when we crawled out the cave? I doubt many cavemen would have drag\ged a woman behind a tree to fuck her if it hurt.
The argument is not silly. You are thinking with modern blinders on.
General comment...
The pleasure centers are reward mechanisms to imprint important life functions. This is why food tastes good, the tongue is designed to reward nutritional intake - which we will die without, and the different specific tastes reward variety ensuring a nutritional balance. This is why sex feels good, the body is designed to reward procreation.
On the reverse, stimuli of pain are designed to protect the body and imprint damage/harm correlation. Cold equals death, we freeze and begin to recognize harm as the blood moves to the core to protect the vitals. Heat burns the flesh, we learn not to touch flames which will damage the body. falling equals pain through blunt trauma, we gain control of our equilibrium and learn not to do that, which makes us more agile and capable of escaping danger. The pain of childbirth imprints the protection mechanism making it seem important, which it is, and activates the short term memory so the mother doesn't simply walk away from a serious event. Further pain of engorged breasts ensures the child will be used to drain them over a period of time where the offspring cannot fend for itself.
This is pretty basic, and everyone knows it on basic levels but you never really hear it described in few words. This pleasure pain thing is replicated through all of nature, and attaches to the other senses as well. Beautiful, go after it. Repulsive, avoid. Smells bad, probably a danger sign. Even if its just your armpits, its still telling you your hygiene is becoming a concern. The problem lies in the visceral reward replication mechanism, people will do the pleasurable things over and over, and avoid the painful things even if they're mildly dis-comfortable. Like work, where the reward is arguably worth less than the perceived pain of a repetitive task.
So saying people would procreate if it was painful in the immediate act is fucking idiotic, because we're not designed that way biologically. Pleasure
through pain is symptomatic of psychosis, negative self esteem, and whatever other shit drives self-harm from the subconscious through the conscious and emerges via physical acts of self destruction. The babies that were born exclusively unto a humanoid race of self-mutilators over generations would burn out faster than a plague, and we would indeed become extinct no matter what tripped out little fantasies your bongsmoked head can conjure at Derp University.