Bigamy and Polygamy probably were outlawed for a combination of at least two reasons: the prevailing mindset of the time that they were by definition sinful, and the realization that bigamy commonly involves deceit, each wife being unaware of the other, and that polygamy commonly involved coercion and subjugation of some of the wives, commonly very young vulnerable women.

If all involved are fully responsible, freely consenting, adults, the validity of legal prohibition is indeed questionable at best.

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