Where in the constitution does it say that one has a fundamental right to marry the same sex? If homosexuals were prohibited from marrying people of opposite sex, then I would buy your argument. But they are not, and they can--and many do--enter into traditional marriages. And many even have kids with their opposite sex partner. So in short, homosexuals have just as much right to a traditional marriage as anyone.
Edit: at least, that's my opinion until the Supreme Court rules otherwise, which they may or may not do. But as yet they have NEVER proclaimed there to be a fundamental right to marry people of the same sex.
This can't seriously be your argument... If I'm reading it right, you're telling me that every gay person has the right to marry someone of the opposite sex, and that if they don't, then it's their own fault for not doing it. Please tell me that I totally misunderstood what you are saying. Pretty please.