Because it's just a benefits grab via govt dictate .Quote from Optional:
But why can't a gay couple have the same rights as a hetero couple? I don't even know what the difference is as it varies state by state country by country.
But obviously there's more to it than "why change anything". Clearly the gays feel like they aren't getting a fair shake at the marriage tree.
And it opens up marriage to be interpreted later as any combination and number of adults , citizenship, pets , farm animals for special rights and privileges.
It also legally presupposes all combinations are equal before the court in family law. Quite frankly it's a silly assumption that men and women are interchangeable.