Forgive me if I'm missing your joke, but most of the American public did think that way. Most of the American public was against war until Japan attacked America. And responding to an attack is not what I would call being "world police". Nor is going to war with Germany after Germany declared war on America.

This is why America entered the war so late. If America were thinking of itself as world police at the time, why did it take America so long to actually go to war?