Augustine in about 300 A.D. was a primary shaper of theological thought and went so far as to argue that sex was sinful even within wedlock unless the specific purpose was always conception! This reflects the need at the time for many more children. Infant mortality was very high and the economic and political structures were based on families.

Thanks to widespread illiteracy - or apathy - whatever the church said was now law. Intercourse was no longer natural and good; sex was dirty and only for procreation. Celibacy was the new standard for the clergy. And it was a great money maker! If you sinned by enjoying sex, you must come to the church for repentance, which required a donation to demonstrate your faith. What a perfect way for the church to raise capital: make everyone a sinner because of innate sexual desires and then offer to absolve them for a sizeable donation.

Making polygamy a "sin" was a slow process. Before the 12th century it was common for Catholic priests to have multiple wives and mistresses. Pope Gregory II in 726 said "when a man has a sick wife who cannot discharge the marital function, he may take a second one, provided he looks after the first one." Later, with concerns for protecting Church property from inheritance, Pope Pelagius I made new priests agree that offspring could not inherit Church property. Pope Gregory then declared all sons of priests illegitimate (only SONS since lowly daughters could not inherit anyway).

In 1022 Pope Benedict VIII banned marriages and mistresses for priests and in 1139 Pope Innocent II voided all marriages of priests and all new priests had to divorce their wives. This had nothing to do with morality (multiple women for males had long been the norm since before biblical times), but it was about MONEY!