The US government should get entirely out of the business of marriage.
The .gov should offer:
-name change
-paternity identification and adoption proceedings (with a fee equal to how much the average job of that type takes)
-allow a person to give another person power of attorney
-allow the same basic system for power of medical decisions
(maybe even call these two together 'designated next of kin')
-dual ownership or merging of finances.
Reform the tax code so there is no marriage penalty or marriage tax break.
You can then leave the marriage rules up to each specific religion. If that's wear white, only allow man + woman, have it at the cathedral with a priest in front of you and a kiss afterwards, so be it. If that is having a community party in your home where you jump backwards over a broomstick 3 times, so be it. If that is a man + man, hey, as long as your church and/or community recognizes it, fine.
Heck, in a situation like this you'd be able to deal with the common family structure of Biological Mother takes in Biological Daughter who herself has a Biological Daughter (Granddaughter of the first woman) where only Grandma has a job. Now Grandma can put both daughter and granddaughter under her work insurance, if mother cannot be contacted Grandma can give medical direction if granddaughter is hurt, if Granddaughter is raised for 10 years by Grandma and Ma, then Ma dies, Grandma can immediately step in as parent without risk of the kid going to the estranged biological father (who would then probably pass kid onto his own grandma for raising) or heck, after 10 years of raising the kid together in the household as a team, if Grandma and Ma have a big fight and decide to go their separate ways, Grandma now can petition the court for visitation rights.
If you replace Grandma in that equation with 'new boyfriend/husband' he has all those rights. As far as raising a stable family, while some combos are more desirable than others, the reality is you get all kinds. Why should a step-dad who raises the kid for 10 years have more rights than the Grandma who raises the kid for 10 years in the eyes of the law.