Well I'm not picking you, I understand your argument about letting in people you don't know because every nation wants to be the best, and you need members for that to happen. I understand that. But there are still precautions that nation leaders can take, like making sure states don't hide their flags, and when they do suicide you have to take the suicider out. If you let people in and they go off harming other nations, and you don't think you are responsible for anything and "it's not your fight" then you will soon find that it is your fight when the victim nation comes knocking at your door.
So I agree it's hard to not let people into your nation but if you don't want trouble you can't let in suiciders and after they leave say it's not your problem.