I'm not questioning homosexuals being upset about it. If I was in their position, I don't think I would be up in arms, but many are, and anyway that's not the point. What I'm saying is the way that frustration is channeled isn't constructive.
In my mind, barring some sort of end of days, there will eventually be homosexual marriage in this country. But it won't come about by some movement to not recognize anyone's marriages or Brad and Angelina refusing to get married until everyone can (previously: "be[ing] douchebags and acting like jerks to counteract other people being douchebags and acting like jerks"), it'll come about in 10-15 years when public opinion is naturally turned by older, generally more socially-conservative, people dying off and being replaced by younger, generally more socially-liberal, people replacing them. That's how social change has always been brought about, gradually over time.
I still think a far more interesting topic is who is in favor of legalizing polygamy and incest marriages, and if not why.