I practice law in Massachusetts and this state was the first in the nation to legalize gay marriage in 2004. While I don't have the benefit of statistics, I believe that I can evaluate the impact of this decision.
The press no longer carries stories about gay marriage in the state. People appear to have accepted gay marriage and no longer discuss the subject. There were never any stories of any harm to anyone in the state. There were no reports of heterosexual marriages destroyed as a result. Basically, all of the fears of harm from gay marriage failed to occur. There appears to have been no negative impact.
Nevertheless, there are some people who were affected by this change in the law. The numerous gay men and women who were able to legally wed and have the same rights and benefits as others were affected. They now can inherit from their spouses. They can obtain employment benefits for their spouses. They are treated the same under state tax laws as other married couples. They have the opportunity to be happier as a result of the equality they can experience in this state.
While the rest of the country struggles with the issue, they should look at the impact of gay marriage in Massachusetts. It appears to me that gay marriage has benefited society and had no negative impact at all.