I think the real reason people in the social circles LWers tend to hang around in oppose poly marriage is because they don't want icky Muslim and Mormon men getting married to more than one woman.
People likely to practice polygamous marriage are low status in our societies, thus we tend to see forbidding that as a good idea. This is how humans work. Everything added onto this is just clever rationalization imo.
thus we tend to see forbidding that as a bad idea.
ITYM 'good'?
I've certainly heard the argument that polygamy is tied into oppressive social structures, and therefore legitimizing it would be bad. Would you say this is rationalization?
FWIW I'm very skeptical of the whole "status explains everything" notion in general.
A thought occurred to me today as I skimmed an article in a rationality forum where the subject of gay marriage cropped up; seeing as the issue has been hotly contested in various public fora and especially the courts, what about poly? After all, many if not all the arguments for gay marriage apply to poly marriage as well.
Questions for LWers who are currently in a such a relationship, or have an opinion to share:
Do polies want to marry each other or do such relationships not lend themselves to permanence above a threshold of partners? Should polies campaign for the right for a civil union anyway? what are the up and down sides of this? etc