Consider this. You live in a state where your relationship is not legally recognized. A nearby state offers marriage equality. If you had the option, would you move to the state where you can get all the benefits of marriage?
For same-sex couples with career flexibility, the answer may well be yes. Faced with the choice of having all the protections that come from a legally recognized relationship, as well as the social acceptance, and having no official recognition of their relationship, couples may well pick up stakes and go, creating a gay brain drain in states without marriage equality.
Bloomberg News cites as an example Hans Bernhard and Mitch Null, a couple in North Carolina raising their one-year-old daughter, Eva. The pair are considering moving to Maryland, where they not only can be married but where Bernhard can legally adopt Eva, an option not available to him in North Carolina. Berhard is a veterinarian, and Null an IT business operations officer, exactly the kind of professionals that states throw tax dollars at corporations to bring to the state.