Slavery is illegitimate, even if you embrace it.
You don't get to suspend my freedom because YOU have decided I can't make decisions for myself.
In case you haven't noticed, arranged marriages and the like are not allowed in our society.
PS, Hillary thinks government should make all these decisions too. She thinks we should all get permission from people with guns to do all kinds of things.
Your model of marriage as simply a contract between two people is ridiculously unrealistic. That is not what it is or has ever been.
Since the dawn of human history in every culture marriage has involved a series of elaborate and very expensive private and public ceremonies. Human societies have always thereby underlined the awesome importance, the sacredness of this institution and the lifetime permanence of the obligations undertaken. It is an institution the entire weight of human tradition and culture and religion and if need be coercive force have backed up. It is and has always been the backbone of human societies and that is more important than your likes and dislikes.
As is normal, human beings look to government to do what human civil society cannot. Civil society can no longer protect women and children in a secular, mobile society without shame or scandal.