For the purest of Libertarians, their answer would be that no nation should limit the free travel and movement of individuals across borders. Such a conclusion is one of the best illustrations why theory must be founded in reality, for it to have merit. If the optimum criteria is to postulate the best of all possible worlds, you better locate to a fantasy planet where you are the sole monarch. In the real world, governments exist and operate by their prime directive - to protect and preserve the STATE.
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