But the government can declare that a man and woman can form a special union and this can be encouraged and recognized as valid and important.
I see no value in giving up and just saying "Whatever you like" to such a crucial institution. I'm a social conservative and proud of it. Government recognition of traditional marriage is a good thing.
By whom? I personally don't recognize a couple as married unless they were married by a priest, minister, or rabbi. Without God blessing the union, in my opinion, it's nothing.