If only. No, it was the government deciding that something was functionally the same as what they were already licensing and therefore they should license it as well.
Government does not have the authority to define, license or restrict personal relationships. That arrogation by government is how the whole mess got started.
Really? So let’s be clear here, you want Islam or the Catholic church to define what legal marriage is? When do you think that the government or some other controlling common authority (including an all powerful church or state church) first got involved in marriage?