That is an absolutely inane stance to take. How about instead of the obviously unattainable and unrealistic goal of "world peace", we just go for "more peace", or "less violent death" or similar goals. It is very hard to argue that American hegemony has not significantly reduced conflicts around the world. Not all of them, not equitably, and generally in pursuit of economic rather than ideological interests, but there is basically nothing to be gained by opening up the US to actually being threatened by competing powers.