And, yes, I know that one of the stated reasons of DOMA was to express “moral disapproval of homosexuality” (but this statement was given only by some members of the House, and it's just false to infer that this is what motivated every voter for DOMA in the House AND the SENATE) Well, that’s just dumb. Even John Corvino, one of the most prominent advocates for the legal recognition of same-sex "marriage" has acknowledged that the morality of homosexuality and the legal recognition of ss’m’ are two entirely separate questions.
“The connection between the morality debate and the marriage debate is not absolute. One can believe that homosexuality is morally wrong while also believing that same-sex couples should have the legal freedom to marry, just as one can believe that divorce is morally wrong while also believing that a free society should permit it. Conversely, one can oppose same-sex marriage without believing that homosexuality is morally wrong (although the position is rare). [What’s Wrong with Homosexuality, p. 149]”
The question of the morality of a relationship has nothing to do with the question of what counts as a marriage. For instance, I think incest is immoral. Nevertheless, I would never deny the possibility of an incestuous marriage. On the other hand, I have nothing against a same-sex gin rummy partnership, nothing at all, but I would never ever say that such a partnership could ever become a marriage.
Thus, opposition to the legal recognition of same-sex "marriage" cannot by itself be "homophobic", even if by "homophobic" we are to understand in its broadest sense as "a moral disapproval of homosexual relations".