Taught, yes, but imposed? In any case, you're ignoring important facts, many of them addressed in a broad view of the Old Testament and the Gospel of Matthew.

Taught, yes, but imposed? In any case, you're ignoring important facts, many of them addressed in a broad view of the Old Testament and the Gospel of Matthew. First, in Genesis, the ideal, created union is given as monogamous. Second, none of the prophets were polygamous. Third, polygamy is usually spoken of disparagingly and as something having disastrous consequences. Fourth, Mosaic law also permitted divorce, but that was a divine dispensation that Jesus lifted and that one existed in the first place because "your hearts were hard". He goes on to say that "it was not this way from the beginning. I tell you that anyone who divorces his wife, unless the marriage is unlawful, and marries another woman commits adultery" (Matt 19:8-9). Thus, polygamy may have been tolerated for similar reasons, that is, as a concession to the times, as it were. Furthermore, Maimonides argues that while the Torah may permit certain behaviors, a synoptic reading would show that it establishes rules that show these behaviors are wrong.