There's this meme out there that the answer to marriage equality is for the state to get out of the marriage business and let it become just a religious notion. This is a bad idea for at least 2 reasons.
First, regardless of what you call family relationships, society will have an interest in various issues that they involve: What happens if the relationship ends? Should remaining partner(s) get more favorable treatment with respect to inheritance than people outside the family? Can 1 partner be compelled to testify against the other(s)? I doubt that many opposite sex couples would want to have to engage a lawyer to draw up all the appropriate documents that some kind of laissez-faire, libertarian view of marriage would entail. What marriage equality demands is that same sex couples be given the chance to have all the rights that opposite sex couples have the chance to get and to get them in the same way: by getting married.
The other reason I think it's a bad idea is that it gets history completely wrong. Its proponents claim that marriage used to just be religious, but until the Enlightenment, talking about secular law, religion, and culture as separate concepts would be hard indeed, even if all talk of marriage had been in religious terms. But I really doubt that it was, anyway. Since marriage was an economic relationship back before the Romantic Era, the secular law would have played a large role in its regulation even back in the day.