But since cognitive dissonance is NOT making their heads explode, here's a little snippet from the DOMA hearings that should make it extremely clear:
Elena Kagan read from the House Report from Congress when it passed the law in 1996, which summarized DOMA's entire legal underpinning: "Congress decided to reflect and honor a collective moral judgment and to express moral disapproval of homosexuality."
Collective moral judgement; enshrined discrimination.
At various times in history, it was the collective moral judgement that interracial couples should not marry; that women should not vote; that humans could be owned; that indigenous peoples should be eradicated; that old women with cats should be accused of witchcraft. Some people still hold those judgements, but we don't give them airspace any more.
Moral judgements change. DOMA, too, will find itself consigned to history.