Many people do not, in fact, have wills. And without a will, and a clear set of legal guidelines, what happens to the children and property? These situations can lead to long, contentious, and expensive court cases. The laws did not come into being because of politicians wanting to exercise greater control over their subjects--they were a result of the desire to have a standardized protocol to use in the cases when both parents died.
Then make a will for goodness sake!!! You’re creating this big dramatic problem where none has to exist!
On a legal level marriage is about managing property and other matters when both are alive and distributing property when things end (via divorce or death). That’s a lot of what the gay marriage folks are looking for, that default legal definition. All of which can be handled with other legal documents (powers of attorney and wills primarily) but you get it for “free” with a marriage license. It became especially true when HIPPA went into effect, if you don’t have a marriage license or medical power of attorney on file and you get sick or injured to the point where you cannot make medical decisions for yourself things get really complicated in a way that’s probably going to result in your death.