If it looks like a duck, quacks like a duck, walks like a duck, then it's a duck. You're conferring everything that is marriage but not calling it marriage. How can something NOT be called marriage when it fits everything that describes marriage?
There are people who use cocaine, drink too much and drive too fast, but the state doesn't advocate indulging in those behaviors. It's a moral and legislative decision on the state's part. In certain states, some homosexual behavior might even be considered "illegal." Of course, it happens, as does other promiscuity, extra-marital affairs, pornography, recreational drug use, chain smoking, and fudging expense reports, etc. However, you're asking the state to take a position to not merely protect these people's rights, but to condone their lifestyle. There's a difference, and I think that's really the underlying issue. There have always been homosexuals and homosexuals living together. So what position should the state take? Should the state say that this is great and on par with marriage between a man and a woman? That's quite a leap in a lot of states. I don't personally think it will get much traction, and I'm not in favor of it, but that's just my opinion.