Is this the gay lobby's argument?
I would reply that the particular cause of homosexuality is irrelevant -- totally beside the point -- because society experiences gayness exclusively as a *behavior*. We don't know someone is gay until they do certain things or act a certain way. Not so with race. Unlike sexual orientation, you can know a person's race simply by glancing at their photograph. This is because unlike sexual orientation, race is something you are rather than something you do.
Now, it's normal and just for a society to pass judgements on people's behavior. In fact, Martin Luther King implored us to judge a man not by the color of his skin but by the content of his character -- i.e. by his behavior. Ending the bigotry of race-based marriage laws was in perfect accord with this, since skin color has no bearing on the things married couples do. After all, a marriage across racial lines can be just as healthy and fruitful as any other marriage. A mixed couple can bring children into the world and be a father and mother for them just as any other couple can.
Not so with a homosexual couple. They can never do these things. And because society has a right to judge and to make laws based upon behavior (i.e. what people do), it has the right to deny a homosexual couple public license for their relationship. Thus the barring of homosexual marriage is in no way harmed by arguments based on descrimination against a person's DNA.
Case closed.
Great points!