I've never heard of a culture that shames people for being too stingy with sex.
Huh? those same cultures (e.g. Western countries in the Victorian Era) did shame people for being too stingy with sex -- they were expected to have lots of children, and so made birth control very taboo (even the calendar method). Not having children (even for men) was considered an abrogation of responsibility. (A president of a Mormon college recently had very nasty things to say about men who are unmarried and over 25.)
In current, conservative churches, one pastor gave a lecture encouraging married couples to have more sex, and I heard about a different such church on the radio that was promoting the same message. (See also C. S. Lewis's discussion of the awesomeness of sex within marriage in Mere Christianity.)
The sex they condemned was sex outside of marriage, which, given the technologies at the time, did have significant risks. Now, there is good reason to debate the magnitude of these risks, but it's not some kind of bizarre phenomenon.
It is a cultural universal that people are discouraged from having sex as often and with as many people as they want to. Every culture I've ever heard of imposes many restrictions on sex. I've never heard of a culture that shames people for being too stingy with sex.
If we assume that culture is adaptive, this means that the human sex drive is too strong for humans in society. Why is this? As sex drive is a phenotypic feature with extraordinarily strong selective pressure, why haven't we evolved to have the proper sex drive?
One reason could be that reduced sex drive is selected for at the level of the group, while higher sex drive is selected for at the level of the individual.