I don't know that we need to go that far. In the US we take the stance that people should be free to do what they want unless what they want to do interferes with other people doing what they want. Where people conflict in their desires is where the law comes in to settle the matter. Whether that system is good or not is an open question, I guess, but it's what we have.

Using that as a rulestick, no one will be negatively impacted by homosexuals getting married. Studies have been done, plenty of places around the globe have tried it with no negative consequences. The courts agree. There's no government interest in preventing gay marriage.