Between the popular vote to take away the marriage rights of same sex couples in California, passing of same-sex marriage bans in several states, and President elect Barack Obama including full civil unions for LGBT couples as part of this civil rights platform, there has been a lot of recent attention on same sex relationships. Opponents of marriage rights for same sex couples generally argue that it redefines marriage away from its current and "traditional" form and that children are best raised by two opposite sex parents. Advocates for allowing same sex couples the right to marry argue that marriage confers over a thousand rights that they are currently denied, like the ability to inherit property, visit a sick partner in the hospital, and provide citizenship for non-citizen spouses. See the U.S. General Accounting Office's report for the full list the 1,049 rights. Advocates also argue that children do just as well when raised by same-sex parents and that marriage provides a number of psychological and health benefits that they are currently denied.
I'm not a historian, but a quick read of the history of marriage makes it clear that it has evolved and changed throughout history and that the current version is a relatively recent phenomenon. That our current version of marriage is not "traditional" invalidates that argument against expanding it to include same sex couples, in my opinion. This leaves the real merits of the debate to center on positive and negative effects of marriage on same sex couples and their children. Fortunately, social scientists have been studying same sex couples and their children and their research provides much relevant information.
Wellbeing of Children One of the most widely cited arguments against allowing same sex couples marriages rights is that it could harm children raised in the context of these relationships. Upon examination of the social science research in this area it is clear that the evidence does not support this argument. According to a report by the American Academy of Pediatrics, "A growing body of scientific literature demonstrates that children who grow up with 1 or 2 gay and/or lesbian parents fare as well in emotional, cognitive, social, and sexual functioning as do children whose parents are heterosexual. Children's optimal development seems to be influenced more by the nature of the relationships and interactions within the family unit than by the particular structural form it takes." Since that report was published in 2002, a number of additional studies have been published showing that children with same sex parents do at least as well on the outcomes studied as children as opposite sex parents. This is why the other major psychological and health organizations have made resolutions supporting same sex marriage and parenting (The American Psychological Association for example).
Last year I did a television news interview about the issue of same sex couples raising children. During the segment they showed a clip of me describing the social science evidence, and then they showed a clip of a religious figure saying that research shows kids are better off with a "mom and a dad." I was disappointed that they showed this clip because I had explained to the reporters that this issue often gets confused by making inappropriate comparisons. In the case of the religious figure, he was referring to research showing that children raised with a mom and a dad look better on some outcomes than children raised by a single parent. Most of these differences are explained by the socioeconomic strain of being a single parent. But comparing children raised by a mother and a father to children raised by a single parent tells us nothing about how well children will do when they are raised by two same sex parents. The appropriate research approach would be to compare children raised by same or opposite sex parents. And these kinds of comparisons make it clear that children raised by same sex parents do just fine. Making other comparisons is, at best misguided, and at worst purposefully disingenuous.
Benefits of marriage. In addition to the legal rights that come with marriage, there are a number of well known psychological and health benefits of being married. It should come to no surprise that having a shoulder to lean on during difficult times, a partner contributing income and effort to sustaining the household, legal protections of your relationship, and a person to help multiple the joys of life has many health benefits. More recently, research has shown that making it more difficult for some people to reap these benefits imposes health risks. The January 2009 issue of the Journal of Counseling Psychology has several articles reporting novel research on this topic. According to the press release for the issue, "Amendments that restrict civil marriage rights of same-sex couples - such as Proposition 8 that recently passed in California - have led to higher levels of stress and anxiety among lesbian, gay, bisexual and transgender adults, as well as among their families of origin, according to several new studies to be published by the American Psychological Association." The release reports results from an online study of 1,552 lesbian, gay and bisexual adults from all 50 states and the District of Columbia. According to the researchers, led by Dr. Sharon Scales Rostosky, at the University of Kentucky, "The results of this study demonstrate that living in a state that has just passed a marriage amendment is associated with higher levels of psychological stress for lesbian, gay and bisexual citizens," Rostosky said. "And this stress is not due to other pre-existing conditions or factors; it is a direct result of the negative images and messages associated with the ballot campaign and the passage of the amendment."
The results of this and other studies suggest that denying same sex couples marriage rights not only prevents them from reaping the psychological and health benefits of marriage, but the process of codifying the elimination of these rights has negative psychological impacts on LGBT people.
Given the scientific evidence of the positive effects of same sex marriage on couples, the lack of negative effects on children reared in the context of these relationships, and the harm caused by preventing or eliminating marriage equality it doesn't seem that there is a solid foundation to stand on when arguing against allowing same sex couples to wed. From my perspective, it comes down to common sense. If it helps some people and it doesn't hurt anyone, why not let it happen. I think the comedian Wanda Sykes put it best, "It's real simple. If you don't believe in same-sex marriage, don't marry someone of the same sex." In other words, why not allow gay marriage?