In October of last year, Pennsylvania Gov. Tom Corbett commented that same-sex marriage is analogous to incest.

As can be expected, all hell broke loose. His opinion was denounced as “hurtful,” “absurd,” “offensive” and “demeaning.” But few of these criticisms were followed by an articulate, rational explanation of why Corbett’s comments were so absurd and offensive.

In an era where the meaning of “traditional” marriage has been challenged and re-envisioned, it is important to consider the wider implications of our society’s newfound understandings. This means more than offering an emotional response, a gut-urge that something is “yucky” or even “offensive” and instead searching for logical conclusions.

Jessica Gerson of The Huffington Post, defending the validity of same-sex marriage against comparisons to polygamy, pedophilia and zoophilia, establishes marriage as between two human beings, both of whom are adults, wishing to form a mutually consenting relationship. Yet despite the thrust of Gerson’s argument, that legalizing same-sex marriage is not a “slippery slope,” it still seems arbitrary to draw the line at same-sex couples.

What about cousins, for one? Our immediate impulse is prematurely dismissive, gagging at the thought or cringing at the comparison. And yet the dilemma still remains. Cousins, like any human beings, are capable of reaching adulthood, forming mutually consenting, loving, monogamous relationships. For the skeptical, it has been estimated that 10 percent of marriages worldwide are between cousins, and estimates the number at 20 percent, with 80 percent of historical marriages, though they operate with a clear bias. Charles Darwin, too, married his first cousin. So did his grandfather. Marriage between first cousins is legal in Canada, most of Europe and 26 states in the U.S.

The most common argument against cousin marriage is an appeal to genetics. Some maintain that for the offspring of such relationships the risk of genetic defect is unacceptable. But, while this argument not only completely ignores sterile and same-sex cousin couples, the risk of significant birth defect in the offspring of cousin couples actually only increases from three to four percent to four to seven percent, according to the National Society of Genetic Counselors. This number is simply not substantial enough to justify banning marriage between first cousins wholesale. If it is, another slew of questions needs to be addressed. Should certain populations more prone to genetic disease be refrained from reproducing? Tay-Sachs, sickle cell anemia, cystic fibrosis – these are just a few of the genetic diseases with ethnic ties. The risk of bearing a child with Down’s syndrome skyrockets from 1 in 1450 to 1 in 30 as a women ages from 20 until 45. Yet few would deny these people the right to procreate, at least not indiscriminately.

In appealing to the genetic argument, opponents of incest who are also proponents of same-sex marriage are forgetting that their definition of marriage no longer includes the ability to produce healthy offspring.

If, then, we as an enlightened society fully legalize marriage between first cousins, even if only between sterile or same-sex couples or even fertile couples after stringent genetic screening, it would still seem arbitrary to limit the right to marriage there. What about sibling marriages? Marriages between parents and offspring? Between aunt and nephew, or aunt and niece for that matter? For Gerson, denying them the right to marriage is denying them their humanity, sanity or mutual consent – granted the consent of the rest of the family might be harder to come by. Of course the genetic risk is much, much greater, but again, there are many cases in which one or both parties are sterile, past the age of childbearing or else otherwise incapable of producing offspring.

Past models of incestuous relationships certainly seem foreboding: sexual abuse, domestic violence and pedophilia are all too often present and will doubtlessly be cited as reason enough to continue the legal and social ban on incest. But there are, understandably hidden, many instances of consensual, incestuous sexual relationships between adults. “You don’t choose who you fall in love with,” says Kathy Hollenbach, happily married to her first cousin. She too thought her spousal situation unusual until her discovery of The fact is, an overwhelming body of human experience persists, showing that loving, consensual, sexual relationships can form. To dismiss them on the basis of their destructive counterparts is to ignore the individuality of involved parties, prematurely denying fundamental human rights.

In a recent debate Lawrence Krauss, an outspoken atheist and a proponent of same-sex marriage, explained that incest wasn’t necessarily wrong: “If you asked me, a priori, if a brother and a sister loved each other and used contraception, is there something absolutely morally wrong with that? … I don’t think there’s any absolute condemnation of that fact, if they love each other and care for each other, and they go off and it doesn’t affect anything else … ” For proponents of same-sex marriage, to simply say that incest is unnatural, barbaric and disgusting is no longer enough – how many times has that language manifested in attacks on same-sex marriage?

Proponents of same-sex marriage rejoice that our society is learning to ignore our emotional impulses and stop appeals to natural order, to forget our adherence to ancient texts, religious traditions and other “antiquated” views.

They claim we are outgrowing our “backward” intolerance for interracial and now same-sex couplings, that we are appealing instead to reason and empathy. Now will we turn around and simply forget these lessons, denying rights proponents of same-sex marriage claim to have made available to all? Is this not, by their modern ideals, a great injustice?

When we watch that scene in Star Wars, where Leah kisses Luke, it makes us cringe: we’ve seen the ending, we know they’re siblings. But if we had that reaction to a gay couple kissing, we would suddenly be shunned as intolerant bigots. It doesn’t add up.

New Hampshire seems already on board on the issue, and is currently considering legalizing civil unions between siblings. As same-sex marriage continues to be legalized across the U.S., the societal certainties of the last century are coming under increasingly critical re-evaluation.

We must begin to ask ourselves, after so much erasing of lines, where the new lines are to be drawn, and why.

Jonathan Warkentine is a College sophomore from Almaty, Kazakhstan.

Photo courtesy of WehoCity, Flickr