Although I’m not for the American 'imperial grand strategy' (an official US foreign policy by the way) and I usually side against it, I feel this argument needs some balance. I think Americans themselves aren’t bad people for the most part but are affected very heavily by Propaganda and the Media, as are we all. Our views and opinions are swayed more than we think by these factors.
America is simply the latest Hegemonic global power, one of a long history of predecessors of which Great Britain has been one in the past, and ironically some of our policies of that era would be considered pretty awful by todays standards.
The point is it's an established pattern in political science that these powers rise and fall, being replaced by another. Americas Hegemony will end sooner or later. God knows who will replace them and I think you'll find that if you look at the alternatives they don't look great either...

Counter to that though, you could say, why can't America with all her global coercion and power use it for the good of the world? Well that would be a liberal ideal. America favours realism - or the belief in power through Military and economic supremacy and didn't get to where it is today using flower power!
Call it waffle if you like but it's all common sense. Second to that I study this sort of thing in Uni for what it's worth as everybody seems to be a political scientist these days!

JZ.