I think it's kind of insulting that you put sexual-discrimination on the same level as racism and sexism. People can't help what nationality or gender they are born as, and until it's proven otherwiese, I do believe that people are able to choose their sexuality. But even in the unlikely event that they're not, sexuality isn't something you see as soon as you look at a person, like race and gender.

Also, I don't think it's a good defense to say that incestual marriages should be banned (and gay marriages not) because they produce defective children. Homosexual marriages produce no children at all, except through artifical insemination. And if an incestual couple really wanted healthy children, they could undergo the same procedure. So in the same light, if homosexual marriages are allowed, incestual marriages should be too. Love is love as you all say, right?