Yeah, but as Maggie so succinctly put it, there is a difference between society and the state.
I fully understand the desire to stand up in front of all one’s peers and say “I love this person (or indeed these people I suppose) and I’m going to love him/her/them for the rest of my life”. I’ve done it. I also recognise the desire for that relationship to be recognised by your peers and wider society as particularly ‘special’.
However, it should not confer and particular rights, or indeed restrictions, in law, and one should be able to do it with whomever they like.
It’s just not the state’s business.