I don’t mean to get too far out here, but I feel that
understanding from where these beliefs came and how
they are promoted will liberate many readers.
Onward.
Anywhere from hundreds to thousands of years ago,
rulers of lands kept large harems of women. These
harems were guarded carefully to prevent any males
except the rulers from having access to these women.
The penalty for sleeping with one of the ruler’s women
could be, in an extreme case, your own death and the
deaths of everyone in your family and village. (Back then
there were bigger risks involved!)
These rulers kept so many women not just for the
sexual variety that it provided them, but also for the
reproductive power that it gave them. These rulers often
had detailed records kept so they could copulate with only
the most fertile women and maximize the woman’s
chances of pregnancy and passing on their own genes.
So what do you think these rulers did to protect their
harems?
Right! They passed laws (from which they were
exempt) to promote monogamy.
In these times there was a great shortage of women,
so these laws would discourage married men (those lucky
enough to find a woman) from seeking sex outside of
their marriage and therefore further protect the ruler’s
harem.
Next, we have the church.
Many religions prohibit sex, make sex ‘wrong’, give it
some name with a negative connotation like ‘fornication’,
or in one way or another discourage it.