Kramodlog
Naked and living in a barrel
Marriage, in addition to its magical effect, is also a form of "contract" (scare quotes used because it isn't arbitrated using contract law). That declaration is acknowledged by the state and according certain privileges and obligations. A couple is a couple before the contract is entered into, but marriage adds a expectation of stability on the part of participants (thus it is expensive and time-consuming to exit the union).
Many of marriage's effects can be at least partly duplicated by other legal frameworks: wills, living wills, contracts and agreements, power of attorney, etc. Marriage as a legal entity is merely a bundled package offered by the state with its own attached riders (like incestuous can't take advantage).
And the state can provide that legal bundle to couples who didn't go through the ritual, like it does in Québec. The ritual is not a necessity. Right now the state discriminates against couples who didn't go through with the ritual for no good reason, like it use to refuse to give that legal bundle to couples of the same gender.
Gender, rituals, ethnicity, aren't good reasons refuse the legal bundle to couples.