Why was monogamy called pagan?

Answer 1

Monogamy was not the traditional marriage arrangement for most of human history - polygamy (multiple females to one male) was the predominant arrangement. Originally, the word 'pagan' referred to someone living in the country, implying a simple-minded, naive, ignorant person. Therefore, referring to monogamy as a pagan tradition (in the Roman times) meant that someone was acting like an idiot by only taking one wife.