That's begging the question: you're assuming that failure to recognise a homosexual relationship is a legal restriction, which really doesn't make sense. I can declare myself King of England, no-one in America will recognise me as such, but that doesn't impose any legal restriction on me.
There's the side issue of all the other things which 'marriage' acts as a legal shorthand for, but that is a side issue.
You're also assuming that discrimination is an inherently bad thing; it is, of course, not. Discriminating between a green and a red light is a pretty useful survival skill whilst driving, for example. Discriminating between reproductive and non-reproductive relationships is also useful; there's a difference.
My own personal view is that marriage is a religious matter, and that the State should no longer recognise it at all. If two men want to say that they're married, that's their right, just as it is mine to declare myself Grand Vizier of the Martian Republic—and no-one should be compelled by violence (which is what the law ultimately is) to heed either them or me.