Our global hegemony ensures stability of trade for the entire world, and that stability is the reason that other countries eagerly trade and generally deal business with the US. Unfortunately, if we back away from our role as world police, the resulting power vacuum will see some other country take up the role at best, and at worst we could see another large scale conflict as emerging powers compete for dominance.
Our current foreign policy is far from ideal, but there is a delicate global balance which would be dangerously upset if we ceased global operations and "world policing." The GP is niave to think that such rosy, utopian intentions would not be taken advantage of by other global players. Look, for instance, at the current posturing by China in the Pacific. Imagine the scaling of their operations if there was no one in our position to apply pressure against them.
Someday, sure. But, globally, humans are still viciously tribal, and some form of enforcement keeps everything running smoothly for everyone. And while Americans foot much of the bill, there is no denying that our benefit is of larger proportion as well.
