The way I see it, society benefits by following policies that encourage stable households - whether or not children are involved.
Personally, I have no problem with allowing two adults who share a home (with or without children in that home) and who enter into some sort of legal commitment to one another (marriage, civil union or whatever its final designation) to have a legal status that would allow them tax benefits, insurance benefits and other benefits that are considered to be part of a traditional "marriage" relationship.
I just don't see that extending the same benefits to same-sex couples in a committed relationship does any harm to society.
I find it interesting that the "study" mentioned in Scat's post indicates that a major cause of the problems noted in the last few paragraphs of the article is household instability. The researchers specifically targeted a segment where "my colleagues and I randomly screened over 15,000 Americans aged 18-39 and asked them if their biological mother or father ever had a romantic relationship with a member of the same sex" and from those who responded positively, they draw specific conclusions. The report gives no indication of how many of those 15,000 answered YES. It also would seem to have a bias towards those who were raised in an atmosphere of greater instability.
...the children of women who’ve had same-sex relationships fare quite differently than those in stable, biologically-intact mom-and-pop families...
It does go on though to say this:
To improve upon the science and to test the theory of “no differences,” the NFSS collected data from a large, random cross-section of American young adults—apart from the census, the largest population-based dataset prepared to answer research questions about households in which mothers or fathers have had same-sex relationships—and asked them questions about their life both now and while they were growing up. When simply and briefly asked if their mother and/or father had been in a same-sex romantic relationship, 175 said it was true of their mothers and 73 said the same about their fathers—numbers far larger than has typified studies in this area.
So out of a number even bigger than their original 15,000 - they found about 250 who had a biological parent who at some point had been involved in a same-sex relationship. Not really a big sample size at all.
And a bigger question for those researchers - they are to some degree comparing apples to oranges, since same-sex relationships have been devalued to such a great degree, and as even the author of the article states:
Let me be clear: I’m not claiming that sexual orientation is at fault here, or that I know about kids who are presently being raised by gay or lesbian parents. Their parents may be forging more stable relationships in an era that is more accepting and supportive of gay and lesbian couples. But that is not the case among the previous generation...
I THINK ONE PRIMARY DIFFERENCE between those who favor greater recognition of same-sex relationships vs. those who oppose it are that those who oppose it somehow think that if the laws remain repressive and/or favor "traditional" male-female unions, the same-sex relationships will disappear, or at least go back into the closet, and that society would somehow be better if that happens.
Those who favor a gender-neutral approach with equal treatment for both traditional and same-sex relationships disagree with the notion that same-sex relationships will just disappear and feel that society is better served if all people have equal opportunity to form stable household units.