Because you don’t have a right to make the laws if you aren’t willing to follow them yourself.  To participate in self-government, you must be willing to accept the rule of law.
            We don’t let everyone vote--not children, not noncitizens, not the mentally incompetent.  There are certain minimum and objective standards of trustworthiness, loyalty, and responsibility, and those who have committed serious crimes against their fellow citizens don’t meet those standards.