The question Why do governments legislate marriage? has good answers about why the State has a [historic] incentive to legislate marriage. I'll briefly state interconnected definitions of marriage mentioned in the answer:
- A spiritual/romantic union of a set of people into a family.
- A legal contract between a set of people (either explicit, or implicitly governed by prevailing laws). This is of course the main Wiki/dictionary definition.
- An economic union of a set of people into a family to promote economic well-being.
- A cultural construct (an evolutionary stable strategy) which evolved in order to both regulate procreation, and to channel lower-status males into supporting and caring for offspring and society.
My question is this:
Given that the first definition is no business of the State, and three others could be handled by the existing tools, (contracts, family support, etc.), why there is no broad movement in, at least the democratic countries, to drop marriage as a legal concept and live with the concept of family instead, (which, as a nice side-effect, could solve many hot issues of today and of near past)?