See this excellent post by Timothy Burke. Reason #9 is important, and has been neglected by most mainstream commentators.
In general, I agree with Tim that one should avoid the cheap rhetorical trick of referring to recent U.S. wars as "imperialist." There may be an abuse of power in these wars, but in the interest of producing a correct understanding it is important to refer to things by their correct name. In this regard, Chomsky's approach, in my opinion, is pretty much useless. It is also worth remembering no one (in the U.S., Iraq, or Europe) would stand for a sustained American colonial presence along the British model for very long. Colonialism as an ideology has been permanently discredited, even in the west.
Watching the news recently with an awareness of the sheer numbers of RPGs and plastic explosives available to Baathist and Shia insurgents in Iraq, I begin to suspect that the version of occupation that is now being attempted has become impossible not for ideological reasons, but because U.S. and Iraqi forces are too evenly matched at the level of street warfare (again, Tim's Reason #9).
I can think of no happy outcomes.