This is not the point.All of this foolishness only applies to people who choose to believe in the teachings of that one particular church. Do you think a Jewish marriage is invalid? Or a Muslim marriage? They would only be invalid to the one church that says they are not. And some people do not care about what that church thinks.
The Catholic Church deals with what applies to the Catholic Church. In order to have your marriage blessed as a sacrament, one has to follow the rules of the Church. If one is not a Catholic but wants to marry in a Catholic service for whatever reason, that marriage cannot be sacramental. If one wants a Catholic marriage, one has to follow Catholic rules.
It's not hard.