In the matter of reforming things, as distinct from deforming them, there is one plain and simple principle; a principle which will probably be called a paradox. There exists in such a case a certain institution or law; let us say, for the sake of simplicity, a fence or gate erected across a road. The more modern type of reformer goes gaily up to it and says, “I don’t see the use of this; let us clear it away.” To which the more intelligent type of reformer will do well to answer: “If you don’t see the use of it, I certainly won’t let you clear it away. Go away and think. Then, when you can come back and tell me that you do see the use of it, I may allow you to destroy it.I was talking to an engineer once who is mostly of a libertarian persuasion, and he hinted once that he leans on the side of caution when it comes to social issues. An interesting perspective from a very "live and let live"-oriented person, but then he deals with guessing at what happens to complex systems when relatively minor changes are brought to bear. Engineers are more likely than many other professionals to respect the existence of Unintended Consequences. At least as much because of experience as due to theory...
~ G.K. Chesterton, The Thing.
Brand, God put that rock there for a purpose... and, um... I'm not so sure you should, um... move it.
~ Stef, The Goonies
It is said that one of the hallmarks of a certain kind of engineer is hubris. It is often the case that a software engineer isn't content to merely maintain someone else's work, and proceeds to tread into the unknown, oblivious that changes he/she makes may be incompatible with the design. Or to change the fundamental architecture unaware that the original architect might have spent a lot more time thinking it through.
And this is what I gather from (one version of) "gay marriage" argument: Unless you know (or can prove) that same-sex marriage is bad for society, you must vote for it or otherwise support it (to the tune of not challenging judicial decrees that overrule the will of the people) because you are insulting homosexuals for no good reason. And there lies the burden of proof in the eyes of the left-leaning social reformer. And what sort of "proof" is available when sociologists form a left-leaning click, determining what questions are posed and how the answers are framed? Are their answers to be trusted any more than the expert opinion offered about polygamy in the case of Reynolds vs. U.S.? Or the consensus scientific opinion on race before the 1940s?
I don't even think one requires religion to explain gender roles, let alone some revelatory religion. Richard Dawkins' Blind Watchmaker creates species that thrive under suitable conditions. Even a person that attributes our nature entirely to evolutionary processes might well entertain the possibility that marriage is an ancient cultural adaptation to reinforce our genetic adaptations for male-female partnership. Humans are much more sexually differentiated than the species that is supposedly most like us: the bonobo chimpanzees. Are we adapted to different gender roles (with men with greater strength and different neural wiring for risk-taking) and is it wise to presume that there are no consequences with monkeying with a millenia-old tradition that is consistent with our genetic hard-wiring for heterosexism?
All the other social experiments of the past 55 years have been so wildly successful in terms of teen pregnancy, marriage longevity, school violence, teen alcoholism, teen drug use, STDs, etc. Freedom, baby, YEAH!