Those who want to change the definition of 'marriage' by dictate of statute say they want 'marriage equality'--they want to have what truly married people have. But forcibly changing the meaning of the word will not give them that; it will only give them 'equality' with something different, something that is no longer truly marriage. They will have 'equality' with nothing, they will have won nothing. They will have destroyed marriage in order to claim it. They will have only its ashes.
As Shakespeare said: 'Tis won as towns with fire: so won, so lost.'
It will also have been destroyed for everyone else.
It is not 'marriage equality' if the State forces upon all married couples a fundamentally different definition of their state of being (particularly when that is done at the behest of an unrepresentative minority). For the State to say to married couples, 'Your situation is no longer unique to you and all the couples like you, it is no longer what all of you committed to for life, it is now just one of many situations, including many that are fundamentally unlike yours', that is forcing inequality upon them. At present all married people are equal, all over the world. If they are made equal to something else their equality will have been destroyed, and because to achieve that the definition of marriage will have been destroyed it will not have created equality for anyone.