So, now that same sex marriage is legal will the gay rights activist now work on getting Bigamy legalize? What about polygamy? And those who wish to marry in the family? Or was it not really about marriage equality for all,but just for them?
Aw, heck! I might as well address the incest issue as well. Why not?
To equate gay marriage, or even polygamous marriage, with incest is disingenuous at best. Manufacturing constructed outrage at worst.
The most quoted reason why incest is not a great thing is procreation. If two people commit incest and have a child, that child has a slightly higher chance of inheriting recessive genetic traits, often negative recessive genetic traits. If a society allows and condones incestual relationships, then over time the recessive trait issue becomes more pronounced, like the classic problems with European nobility.
However, part of the argument against gay marriage is that marriage is all about procreation and gay people can't procreate! Well, within their marriages, anyway. Part of the argument FOR gay marriage is the acknowledgement that, no, marriage isn't actually all about procreation, but is rather a legal contract between two adults sharing resources. Procreation is an important part of marriage, but you can be married without procreating at all . . . plenty of folks do it, both straight and gay! So that would seem to give the OK to the idea that two close family members can get married, if having kids isn't part of the agenda. Of course, writing a law to allow incestual marriage only if the couple agreed to not having kids probably wouldn't work out all that well.
But there are more reasons than simply procreation to discourage incestual relationships in society. The science isn't completely solid on the subject yet, mostly because incest isn't a popular research topic (for obvious reasons)! But the little science that has been done seems to back up "common sense" that incestual relationships, even fully consensual ones, are often psychologically damaging to those involved. We are wired to psychologically see a difference between our close family members and everybody else when it comes to sexuality and procreation. There are outliers, there have been incidences of adult, consensual, incestual relationships that have seemed perfectly healthy (to the claims of the participants and outside observers), but those seem to be very few and far between. Then there is the documented phenomenon of siblings separated at birth, meet later in life not knowing they are siblings, and being STRONGLY attracted to each other . . . there needs to be more science done on this unpopular topic!
Personally, while I think fully legalizing gay marriages and polygamous marriages is the right thing to do, I feel that legalizing incestual marriage is a bad idea . . . based on science, not on ideology. However, I wouldn't criminalize adult, consensual incestual relationships, I just would not give them the stamp of approval from society with legal marriage.