It depends on the way the anti-incest law is written in each state.
Some state laws are written in general terms: “No person shall marry a parent, child, sibling, first cousin, …”. So such a law would apply equally to same-sex marriages.
But in other states, the law is written in more specific, sex-linked terms: “No man shall marry his mother, daughter, sister… and no woman shall marry her father, son, brother, …”. Such a law would not apply to same-sex marriages, since it doesn’t prohibit a man from marrying his brother, for example. Those states would have to amend their incest laws to cover same-sex marriages. Which would probably happen quickly, after some couple tries to take advantage of this loophole – probably when a local Clerk of Court refuses to issue them a marriage license.
(A similar thing happened here in Minnesota. Our state law in 1969 was written in a general way what would have allowed same-sex marriages. But when Jack Baker & Mike McConnell applied for a marriage license, the clerk refused them. So the judge in Baker vs. Nelson had to fall back on saying, in effect, everybody knows gays can’t marry and quoting the Bible. And the Legislature promptly changed to law to specifically say that.)
Example #1 Gay man marries gay woman, for tax purposes. They have no intention of ever having sex, let alone reproducing. This is a “gay marriage”. It’s legal in all 50 states. But it’s not a same-sex marriage. Is it legal if they are siblings? No.
Example #2 Man marries man or woman marries woman (sexual orientation not relevant) , for whatever reason. This is a “same-sex marriage”, and it’s only legal in a few states. Is it legal if they are siblings? I very much doubt it.
I’ll bet 10 to 1 odds that the legislators who wrote the no-you-can’t-marry-your-sister laws didn’t bother to put in an exception for people who can’t or won’t reproduce.
Well, once upon a time nonmarital sex was itself illegal, so way back then it would have been relevant.
And remember that opponents of marriage equality were in fact bringing it up in the course of the political argument – saying that if we allowed same-sex marriage we would have to allow polygamous, incestuous, pedophillic or even bestial or inanimate-object marriages.
This would be one of those things where the court would send down a fast and unanimous “Come on, NOBODY meant THIS, and you KNOW it”.
I wasn’t talking about laws, I was talking about what is considered “normal” and acceptable. I did, quite explicitly, distinguish between law and taboo in my post, if you had been paying the slightest attention. Most contemporary Americans seem to consider first-cousin sex and marriage to be very icky.
Many icky things are not illegal, and, indeed, where something is considered icky enough, it my not be felt that there is any need for laws against it. (I do not know if it is true, but there is a story that laws against lesbian sex - as opposed to male homosexuality - were not enacted in 19th century Britain because Queen Victoria found the very idea too icky to contemplate, or to believe that it could possibly really occur.)
Oh course, in many societies, ranging from 19th century upper class Britain (and very likely America too) to Australian Aboriginal tribes, first-cousin marriage is considered not acceptable, but practically de rigeur.
All kinds of laws have been made against “icky things”, generally under the guise of “disgusting acts” or some such, which leaves the definition of “icky” or "disgusting " to the pleasure of the courts.
strong yes. Irrational? I dunno about that. The genetic reasons are plenty enough, but there’s more to it than that. Ultimately, you should be able to have a loving, endearing relationship with siblings without getting into sex. Moving into a sexual relationship would clearly not be a good idea, for the many obvious reasons that could also be applied to the troubles that open marriages can face or dating a roommate or hall-mate, etc.