I don’t oppose same sex marriage for religious reasons. Same sex marriage has not ever been adopted by societies going back to the beginnings of civilization, for the very good reason that marriage and family have always been important to the continuance of civilization. Family structure has been somewhat flexible throughout the millenia, but never flexible enough to encompass same sex marriage. Sexual complementarity has alway been a pre-requisite.
Carle Zimmerman took 800 pages in his book “Family and Civilization” examining family structures going back millenia. If you can find the book, get it. In all those millenia of civilization, he finds only three instances in which family structure got so out of whack as to threaten the existence of the societies in which those abnormalities occurred. And the third one he places at the present.
Family structure does not exist in a vacuum, with no effects on society at large. It has serious effects, which can be good or bad, and the decline of family structure can threaten the existence of the underlying society. Same sex relationships are not the only or even the chief malware affecting the family, but it is indicative of how bad things have gotten. I’m not too hopeful that recover is possible.