I believe we give them out so as to give the MoRS a better idea of our identity; one IP address cannot have multiple UN nations, so by asking what it is it becomes simpler to ensure that one person does not obtain multiple Citizenships, seats in the Senate, etc. in order to take advantage of the system or gain undue influence.
(It's my impression that most of our Senators do have a UN nation in NS, Delfos. ^_^)