Should polygamy be legal?

Polygamy is the practice of marrying multiple spouses. Worldwide, different societies variously encourage, accept or outlaw polygamy. So is it unethical? Should it be legal?

Pro

 * Everyone should be free to do anything that doesn't harm others. If it is a free choice between the parties involved, marrying multiple people doesn't harm others and should be allowed.

Con

 * When polygamy is allowed, polygyny (one man, many women) becomes more common than polyandry (one woman, many men), so in practice a polygamous society leads to a polygynous society, which violates the dignity of women.
 * Polyandry could also violate the dignity of women through the mechanism of spousal abuse. Monogamy has been shown to violate the dignity of women in some circumstances too. Therefore, this is an argument against certain kinds of cultures, independent of the parity of unions, not against polygamy in the most general sense.
 * Polygamy leads to some people having no spouses because some have more than one, which generates resentment and destabilizes society.
 * There's also some people with a lot of money and others with none, which generates resentment and destabilizes society, but (in liberal economies) we don't forbid people from having a lot of money just because other people can't handle it.
 * There are proposals to do just that, some implemented, so it is an inapt analogy.
 * In monogamous society there are also people with only one spouse while others without, and that doesn't cause particular resentment or social instability.
 * Polygamy implies that each spouse gets only a fraction of the time, attention, resources and love of their partner.
 * This is true for all relationships. People have multiple family members, multiple friends, coworkers, etc. that they split time with. In these cases, having more members within a group is typically seen as a positive because it creates diversity.
 * If a person can marry as many people as they like this will render marriage meaningless. Every adult person could in theory be married to every other adult person infinitely.
 * A person can engage in sexual relationships with as many people as they like, but not everyone is constantly having sex with everyone else.