“If heteros can deliberately choose sterile intercourse -— unnatural sex -— so can gays and lesbians.
That’s what they say.
“
So what? The act of sex is not the act of marriage.
“And there’s a certain logic consistency there. People across the board -— gay and straight -— have largely chosen against natural sex the way God made it.”
Then tell them that they have thus also chosen against the whole propose of marriage.
Ask them why they should want the burdens of the legal bonding of the institution of marriage when their desire for a relationship is so clearly based exclusively upon their own feelings for each-other?
“I must say, the Catholic Church is the only group I know which has a coherent teaching on this.”
Perhaps because the Catholic Church has retained a consistent and logical understanding of the nature and propose of marriage for thousands of years.
Homosexual acts aren't even "sexual unions" because they don't even "unite the sexes", fer Pete's sake.
As Richard Rodriguez says, the problem is, two gay men just don't have a kosher place to stick it.
British law just discovered that even though gay mariage is legal, two men or two women cannot consummate a marriage, as defined by law.
Neither can they have a marriage annulled because of inability to perform sexual intercourse, because they are not anatomicaly equipped to perform sexual intercourse with each other.
Neither can they be divorced on the ground of adultery if one partner has some kind of sexual jiggery-pokery with another person of the same sex, because whatever they did, it was not adultery as the law defines adultery.
Confused? Yes. Unnatural? Of course. Absurd? Fo' shizzle.
My point, however, is that many heterosexuals do the same. It's all part of the deconstruction of sex, which is a big part of --- in C.S. Lewis' memorable phrase --- "The Abolition of Man".