“That vitiates marriage to the point where is is disappearing among straight people (half of the children born to women under 30 in 2011 were born out of wedlock).”
Laws & attorneys destroyed marriage between straight people; when T-shirts are sold asking: “Why get married? Find a nasty lady and buy her a house.” that says about all we need to know about the state of marriage today. Till boredom or the slightest setback do we part (with the financials stacked against the guy).
“It also tends to redefine marriage as something which essentially “about” the gratification of adult desires, rather than something that is essentially “about” creating a family by begetting and raising children. That redefinition suits the ideology of gay marriage to a T.”
Separating the sexual act from procreation isn’t the root of “homosexual marriage” (though they come to the same conclusion - no children); it is simply another symptom of the post-Christianity period of our history. “Homosexual couples” often like to buy children to “play family”.
You refer to the fact that some gay couples like to acquire children and "play family" as a kind of accessory, an expensive luxury like raising prize dogs. But before the triumph of the contraceptive mentality, having children wasn't just a lifestyle option: it was a physical fact, one of the central facts of sexual commitment. That's why the urgency of "commitment" was there at all.
If it weren't for small dependent human beings being generated from sex, nobody would have ever thought of marriage. It would never have been invented. Why would people ask for religious solemnities or civil licensure or social approbation, for doing sterile jiggity with their excitable bits?