I don't think scrapping state sanctioned marriage would require a total rewrite of the law. We already have existing contract law to cover the binding relationships people might enter.
I guess there would need to be some changes to the tax code for joint filing, to how Social Security benefits are assigned, and to the spousal immunity privileges in trials. None of that seems too significant. Is there any other area of the law that would have to be rewritten in a significant way?
Currently, family law is based on marriage rights. State sanctioned marriage. So if you get rid of state sanction marriage then the basis for family law and parental rights is GONE!
Current contract law does not cover parental rights or children in any way. So what laws would custody arrangements and parental rights rest on if there were no marriage? No body of centuries of common law and marriage law supporting your right to raise your biological child?
I’m sorry you don’t get it, but this is a camel’s nose issue and you are confused about the legal ramifications if we were to allow them to do away with thousands of years of tradition and common law.