Pillory? Oh, you mean like adding a person to the nation then pillorying to them?
That is a legitimate problem that I had not thought of. However this doesn't make the idea lousy.
Adding people into nations against their will is a problem in general, not just with just idea. The solution to that, is when a person is added, prompt a message on their screen saying "<account name> wishes to add you to the kingdom of <kingdom name here>. Do you Accept? Deny?" If the person denies, an add attempt can't be made for 24 hours for that account.
Not only will this fix the abuse in general, but will also prevent the abuse from becoming a problem with any later suggestions as well.