There's been a lot of blogosphere hand-wringing over polygamy lately, occasioned by some polygamy-themed TV show I don't feel a need to see called "Big Love." Much of the hand-wringing comes from people who embrace the libertarian arguments for gay marriage, and then have problems applying the same principles to polygamy.
The non-libertarian perspective is oppressive, while the hard-core libertarian is unrealistic. The Reasonable Libertarian approach is better - we agree that adults should control their destinies, but accept a transitional period where young adults assume their autonomy over time, and don't acquire full rights until the end.
1. No one under the age of 25 can be in a polygamous marriage.
2. Everyone in a marriage must consent (or be divorced) before an additional person is added.
3. Economic benefits from society (like survivor benefits from Social Security) are given to only one person or are divided proportionally among a person's spouses.
The age limit and consent provisions would prevent much of the exploitation we see with polygamy, and dividing economic benefits would stop it from being unfair to the rest of society. Yes, there will be some 25 year olds who will enter exploitative relationships, but at that age one can say it was much more of a choice than for an 18-year old.
I expect in modern societies with modern education, modern life spans, and modern divorce rates, the specter of countless "unmarriageable males" who can't find a wife and degenerate into warlike behavior is also unlikely.
Is this really so hard?
P.S. Krakauer's book on Mormon fundamentalists and polygamy, Under the Banner of Heaven, is excellent.