(I have to admit, at this point I was confused by his response.)
But there is nothing to be confused about. Vacuously, you share the same right: you have no right to marry a person of the same sex, and neither do they. They are neither granted a right you do not posses, nor are they denied one you do. Your friends "logic" actually proves your point.
My advice in debating liberals is that first and foremost you do not accept their premises. This is the distinction between conservatives who know what they're doing and confused conservatives, like, for example, most Republicans. Homosexuality is a mild form of mental illness for which we currently have no generally effective treatments. Being a homosexual is not in itself wrong; but the practice of homosexuality is regarded by most religions as immoral. Your friend is not entitled to define the practice of homosexuality as moral any more than you are. If you believe it's immoral, you do not need to accept his proposition that its practice ought to be allowed. Society expresses its sanction for various practices through law. The claim that one cannot legislate morality is crap. Almost all of our criminal code is in fact a legislation of morality in one form or another. If you accept his premise that homosexual behavior is not immoral, you have no place to go. If you deny his premise, assume that it's wrong, then there is plenty of room to argue how society should regulate behavior it believes is improper.
Our culture is so thoroughly corrupted by liberalism that it's often nearly impossible even for conservatives to see why conservatives are opposed to liberal ideas. The first thing you need to do in arguments is to check your premises. Invariably, you will find that you've already accepted the basis of the liberal position as a starting point, and that is the best way to lose an argument.
Thank you for your response. Vacuous was the perfect word (in more than one sense) for describing Dave’s argument, and the reason why I was confused. I really didn’t know what to say back to him because there was no substance to what he was saying and his logic was flawed by affirming the consequent (if A followed by B is true, then B followed by A is true.
The problem that I have most with liberals is what you describe: I live by a moral code that they do not accept. Lacking a moral code allows them to make their own as they go along. Because I have my code, I don’t accept their premises, although this is sometimes very difficult because they call you names and they are not based on logical thought. I just try to point out their hypocrisy (i.e. “accept gays, but hate religion).