The purpose of government supported marriage is to encourage the formation of family units. Every study I have ever seen has shown a healthy family unit produces more productive members of society. Governments exist for the sole purpose of continuation of their ideal society. Government sanctioned marriage also provides a platform through which a person automatically receives certain rights that make navigating through societies legal requirements much easier. I know this very well....In the military, many of the "married" rights that civilians enjoy, I don't. My wife cannot have our household goods shipped through the service. She can't register our cars. She can't renew her I.D. card without me...etc, etc.