"the power of marriage lies in its capacity to establish collective rules of conduct that help reinforce our commitment to our spouse when temptation calls." -Nathaneil Frank, professor at NYU, nf15@nyu.edu

So the good professor believes marriage is important not because one person's love for another but for the handcuffs put on the marrried wrist? This is part of the bio-argument that many self-described "intellectual elites" believe when they devalue marrriage by defining it by what marriage prevents one from doing. I think marriage is most important because of what it allows us to do.
That is to say, we stand before our spouse and proclaim a higher abstract belief that the sum of our union is greater than our parts. What we do as husband and wife is far greater than what we can accomplish individually.