You don't have to be religious to notice that exclusively vanilla heterosexual marriage has been common to all advanced societies. There are plenty of other models, but any culture that rose to power picked the one.
It seems to me perfectly reasonable to assert that there will be unknown consequences to screwing with a system that has worked reasonably well.
The last time marriage was tinkered with back in the 60s, no fault divorce and alimony as normal were tacked on. Infidelity was also decriminalized. I find it very easy to believe millions of broken homes and fatherless children were a direct consequence. The social consequences in lower socio-economic strata have been severe in a way that educated people generally don't comprehend.
In conclusion, the conservative impulse to "conserve" social institutions that have a long track record of success is not fundamentally religious. It comes from the same place as environmentalism: don't go screwing with complex systems you probably don't fully understand.
Why don't we apply to the same logic to every potential decision? Many Republican tax cuts have been unprecedented, so (il)logically conservatives should have opposed them. The iPhone is a disruptive technology will have "unknown consequences", so clearly it should be banned.
The reason we don't apply this idea (except to things we already disagree with) is because it's completely illogical. Caution is one thing, but simply dismissing every idea that could have "unknown consequences" is a great way to make sure that literally nothing gets done. It is certainly not rational. It is, in a word, FUD.
It's about as similar to social institutions as marriage is to divorce, which you tried to equate. Probably more similar, actually, since marriage and divorce are opposites while communication is a keystone of society that's intimately involved in most of its institutions.
At any rate, saying America's current implementation of marriage is a social institution going back through all of history and geography is just plain weird. Even in the modern age, marriage means very different things to different cultures, and that's ignoring all the "marriage" constructs that have existed in the past. Outlawing polygamy was a greater offense to the history of marriage than allowing gays to marry.
It seems to me perfectly reasonable to assert that there will be unknown consequences to screwing with a system that has worked reasonably well.
The last time marriage was tinkered with back in the 60s, no fault divorce and alimony as normal were tacked on. Infidelity was also decriminalized. I find it very easy to believe millions of broken homes and fatherless children were a direct consequence. The social consequences in lower socio-economic strata have been severe in a way that educated people generally don't comprehend.
In conclusion, the conservative impulse to "conserve" social institutions that have a long track record of success is not fundamentally religious. It comes from the same place as environmentalism: don't go screwing with complex systems you probably don't fully understand.