Same Sex Marriage

"We're going to use a totally new method of building a major suspension bridge. We're using a giant cross. Crosses are holy in Christianity and therefore the bridge will be sound."

We don't allow ideology to circumvent the normal proof of soundness in engineering. Why would we allow someone to change the most important structural element of civilization simply because it's ideologically correct?

As far as I know, all successful large scale civilizations that have independently developed over the last 10,000 years have had the concept of marriage between a man and a woman (sometimes more than one woman). Why is that?

Civilization is more complicated than we can imagine. We don't go around re-engineering the human body without knowing what we're doing. Why do the same for something orders of magnitude more complex?

The burden of proof lies on those trying to do massive structural social engineering. Nothing remotely adequate has been demonstrated to me yet. So I vote NO.