Because words, and mental order, mean things.
I disapprove because
a) Marriage is (by definition) between a man and a woman
b) Homosex is a symptom of deep mental disorder, and is not done by well-minded people
c) As (see b), above) they cannot be fully sane, queers cannot be good parents so
d) Queers shouldn't be allowed to have children by the State, if the State has any role in the adoption of children
e) if you want to have a civil union that's fine . . . but it's not a marriage
Buggery is an evolutionary dead-end engaged in by sick people. If you want to have some sort of officially sanctioned economic union between people based on a criterion of their choice, fine. Don't let it be one where they can screw up the heads (and bodily orifices) of small children who never did anything to deserve it. Union based on double-donging it? Fine. Based on being cousins who take care of each other? Fine. Tax advantages for everybody (or nobody)! but it's not a marriage