It’s not meaningless, it’s just open-ended. Recognizing something doesn’t require defining it in law. For you two examples, the answers are, “Yes, you’re married to X and to Y, because you and they say you are”, and “No, you’re not married to a 12-year-old, because the 12-year-old isn’t legally able to give consent.”
Remember, I said X has to also say they’re married to you, and someone who isn’t legally competent to make such decisions could not, therefore, be married. So, X is too young, X is in a coma, X is senile, sorry, no (new) marriage for you.
Register marriages like copyrights. You can copyright almost anything, and the government doesn’t make any judgements on whether or not it’s a good book, just that it’s a book you wrote. If two (or more, why the fuck not?) legally competent adults want to register a marriage, then it gets registered. The only government intervention is in determining if they people involved are legally competent.
And note, we already do that with essentially every other legal contract in the world. If you walked into court with a contract saying I give you all my stuff, but it was dated on a day I was in a coma after a car accident, or something, the government would have no difficulty telling you to sod off, even if such a contract would otherwise be legal. People act like marriage is somehow fundamentally different, but that’s just an emotional response on their part. No reason for a disinterested third party to get all atwitter over it, though.
…and decisions will be made based on the registered marriage document, just like a contract dispute.
Sure, if you ask the government to step in. Not because it’s the Catholics Vs. Homosexuality, but because it’s “Registered marriage” vs. “Do your job”.
And note, I’m not taking “No Position” on marriage, I’m taking, “All consenting marriage is valid.” These guys are probably trying to be wishy-washy to avoid offending anyone, but I’m not.