California's legislature crossed a significant threshold when it created the status of Domestic Partners, essentially giving non-married persons [gay or straight] most of the rights and responsibilities of married persons. From my view, it is only a matter of time before courts rule there is no legitimate distinction to deny registered partners all rights of married persons simply because some of them are of the same sex.
Demographically, the younger you are the more likely you are to believe there is nothing wrong with gay relationships and gay marriages. From that standpoint, it is only a matter of time before electorates will turn out to approve them.
While religious organizations can turn out their members in droves to barely prevail on measures like California's Proposition 8 in 2008, there's is a long range losing strategy. With Rush Limbaugh looking for a fourth wife, Newt Gingrich on his third marriage, and countless rich old men marrying women less than half their ages, it is hard to argue there is much "sanctity" left in the concept of marriage [or that the purpose of marriage is to raise children to maturity]. Both on a personal and professional level, I've met many people who had unfortunate marriages to those who preferred same sex partners, but weren't allowed by society to live the lives they wanted and wanted or needed the benefits of marriage - they created much pain as a result. These fictions should stop.
I used to believe that a marriage should be between a man and a woman, since here is a reason for children to grow up in intact families - that isn't really what marriage is any more. Today, it just no longer matters to me who has marital rights. I'd just as soon people were happy, one way or another.
It would be nice if the battle were not used to bring out voters for other purposes, and were not so hostile and polarizing. Societies change, and we need to accept that and move on to more important issues than who is having sex with whom.
Of course, as many have said, why shouldn't gays be entitled to be as miserable as everyone else? Or as happy? Or as stable?