I think the question and the answer reflect the misapprehension that you can manipulate people into doing what you want, without coming out and saying what it is directly, because doing so is "mean". So, the hosts frantically try to figure out how to cut Jim's inviting off, without ever once telling him, "Jim, this is not fair to us, or our guests, and we want you to stop doing it. Do not invite any strangers to our party, because we will not let them in."
Meanwhile, Jim continues on his clueless way, probably congratulating himself for making the party so much better for everyone.