Martin Luther approved of polygamy

Luther and Melanchton - who were not opposed to polygamy on principle - granted Philip von Hesse a bigamous marriage in 1539, on condition that it would remain secret.

It almost happened. The Protestant Reformation nearly stayed true to principle. If Christ's bride was a universal catholic church, then monogamy must be correct. But if Christ's brides were the various denominations, perhaps even the various local churches (the New Testament model), then polygny was just and righteous.

Luther and Melanchton knew that this was a political hot potato, thus their request to keep it a secret. But they had no objection in principle. They were both right and wise. Unfortunately, modern followers are not nearly so righteous or wise.