[FlannelPancake]

Incest - maybe. There's a clear harm involved there (inbreeding depression) that's much more substantive than anything used to argue against gay marriage.

Polygamy - We probably will revisit our stance on polygamy in decades to come. Historically it's been used in a way that's profoundly imbalanced towards women (i.e. almost exclusively polygyny), but it's not hard to imagine a future where that's not the case.

[pgeorgi]

The risk to offspring is definitely higher with certain genetic diseases than with relatives.

The case against incest can be made on that base when eugenics are re-established and codified into law. As-is the only argument that holds water is "yuck" - one that same sex marriage proponents should be vaguely familiar with.

[matt-attack]

> There's a clear harm involved there

You conflation of marriage with breeding should be rethought. I suppose infertile couples should be allowed to marry since they cannot bear children?

[raisedbyninjas]

Also brothers, sisters, mom and daughter, nephew and uncle

[anonz_]

> Historically it's been used in a way that's profoundly imbalanced towards women (i.e. almost exclusively polygyny)

Any biologists care to chime in on this? It cuts both ways, and is more complicated than that.

I don't understand how polygamy is imbalanced toward woman. They get a stake of the alpha's attention and him providing for them. In the current system, it's AFBB. The beta male foots the bill for alpha seed.