Because you have agreed, implicitly and in concert with your fellow citizens, to live in a polity with rules around how members of that polity interact with mem

Because you have agreed, implicitly and in concert with your fellow citizens, to live in a polity with rules around how members of that polity interact with members of other polities in order to collectively wield the power of your polity for the aims of that polity. You can try to change the direction your polity takes with its stances towards others. You can leave if you don't approve of those stances and see no signs of changing them. But the question belies a fundamental misunderstanding of...yanno...why polities, why politics, exist.