If the world had no borders, where would production happen? In the place where it could be done at lowest opportunity cost, benefiting us all?
Why do the addition of artificial political borders change this self-evident distribution of production. Why would we ever want to raise prices (by tariffs or other trade restrictions) for no reason at all?
Everyone,everywhere,needs jobs. Why would we not want them all to have the best (and highest paying) job they could ?