It's just the end result of years of influence by depraved religious cults and fascist forms of govt that have been around for years.
Their "anti-sex" ideology is just a normal part of all authoritarian cultures (ex. Communist China bans all internet pornography claiming that it is "immoral and harmful to a productive society" - sound familiar?)
The reasons this wacko view originated are:
1. Ancient cultures like the Israelites believed in "ethnic purity" and "purity of the bloodline" (they disapproved of marrying outside their race, and most marriages were arranged and done for "family honor") - so they invented laws which strictly vilified a lot sex practices in order to keep their race and families as "pure" as possible.
2. Authoritarian/fascist cultures have, throughout history, tried to regulate and control sex. This is because the more they can limit people's individual happiness, the more the people will depend on them (the state/church/Furher/People's Republic, etc)
It's all the same, it's been a common part of history, and it's never had anything to do with "morals". Ever (unless servitude to the state = "morals"). Everyone knows this, and everyone has known it since the dawn of time. The history of human society proves that. Even in countries where looking at a woman without her burka on is punishable by beheading, it doesn't change people's natural animalistic instinct to have a good ****, even if it means losing you head after. But don't try explaining that to social degenerate like Christian right, Communist Chinese, Govt. of Iran, etc. These people are brainwashed and lack the capacity for critical thought - and they've been conditioned to be this way over the years.