David, it may be about "rights under the law" but you are wrong to say that it is that and "nothing more." For some it may be only those "rights" but for a great many (especially the activists) it is definitely about acceptance, too, (or often, only).
If the homosexual activists are not about to destroy marriage, that will be the outcome anyway. ¿Do you care that marriage will be destroyed? I guess the question is "what is marriage", and I admit that I'm arguing for "one man-one woman in permanent and exclusive relationship including the sexual relationship.