I find it interesting how the US is "accused" (is that the word) of not helping the world fight against evil / tyranny in WWII, rather of serving self-interest, because the US had to be attacked first. At the same time, I get the impression that most people think of the US as meddling in world affairs where we don't belong (e.g., Iraq). That just seems a little two-faced to me.
Well, in WWII had tyranny stayed at home
no one would have done a thing (Franco died in his bed), and something has to trigger a reaction. So I agree with you there.
Iraq, ah, let's look at it from the standpoint of serious analysis instead of that of (existing in some circles) knee-jerk anti-Americanism. It breaks into three arguments:
1) Iraq was a menace to no other country, so intervention was little grounded (and a wide majority of the world thought like that). True, Saddam was hardly a loving father to his people, but the principle that a recognized regime can be attacked merely to enforce a change because it does not suit another is liable to justify a possible future misuse. Iraq was a terrible state, but it was not the only one, and if there have to be rules for international policy how will they be taken seriously if the world's superpower will happily do away with them without a serious reason? The problem is, WMD weren't there: who could blame the world opinion when it thinks that oil was behind it?
(Personal note: I'm not saying atrocities can be condoned: America's intervention in Bosnia was a splendid case of using force to do the good thing, something that the EU could not or would not do, and every American should be proud of what you did there. But context matters, which leads to point 2).
2) Iraq was and is a complex place, with a dramatic history and deep internal divisions, all within an even more complex scenario even only within Islam (Sunnite vs. Shiaite, with the topping of the Kurd question). Iraq is now open to the pressure of several different forces, causing further instabiilty in the area as the factions and their sponsors from outside push for their own. But more, now the country is in anarchy and fertile ground for terrorism - this after the intervention hardly improved the West's image in the Muslim world. Who could say with a straight face that Iraq and its surroundings are now safer and more stable than they were? Did the invasion help create better international relationships? They even created a rift within Nato! (Although, like the possible scenario of the USa coming to help an ally, I 100% believe that should push come to shove every nato country would immediately rally around the Stars and Stripes; the best families fight, doesn't mean they won't help each other in need...)
3) Final point: this kind of intervention is made very close to us. And indeed, should things get heated, we're much closer to the line of fire than the USA: unless, say, Iran has missiles capable of reaching your shores and I haven't heard about it. Even accepting that it was done in good meaning (I accept that regarding the American public opinion, much less regarding the government), it's playing gambles on our doorstep. Can you see why we're somewhat apprehensive about it?
(Personal question on the political engineering. Could it be that the USA is still under the idea that what they did in Japan is appliable anywhere: that exporting a democracy is possible everywhere, and that it will be gratefuly accepted both by the laymen and the powermongers?)