Anonymous wrote:1. Because polygamy is often - though not always - connected to coercion/abuse of the women and marriage of underage women.
2. To protect the children that would be raised in polygamous households.
3. Common property right and the benefits related to marriage would be murky with multiple spouses all having equal claims. Wife #1 has the same rights as Wives #2 and #3 in the eyes of the law.
Plus there is almost no way to ensure a balance of power since most commonly it is one man and several women; by default he has the relationship with each of them, they wouldn't have legal relationships among themselves as wives without him. All power over the relationships rest solely with the person at the center. The issues with property rights, inheritance, decisions on medical care, etc. would be extremely difficult to enforce.