system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do most societies associate sex with shame if it feels so good? And why not other "feel good" stuff?

This post is assuming religion is human-made.
gpt
Prior to the development of reliable birth control, there were some pretty major consequences associated with sex (stds, kids, etc).  It was beneficial to discourage recreational sex, and shame is a good way achieve that.  Nowadays sex is mostly safe, but society is slow to change and so those shameful attitudes still exist.