From my point of view, many of these discussions are based on two modes of thought:
1) The world as it is
2) The world as we'd like it to be
If we can't agree on #1, I'm not quite sure how we'll ever get to #2.
In keeping with the KISS (keep it simple, stupid) method, I'd like to break down some basics:
a) The U.S. (as is every country) is self interested. Our people before others, our needs before others.
b) The stronger the nation, the more able to ensure their interests are met.
c) The process by which any country tries to keep it's interests at heart can be ugly, mean, and destructive.
d) If any country does not look out for itself, there will be others taking advantage of it.
e) As of right now, there are limited resources in the world.
I'm basing the above on history. Any history of any culture.
Now, I would argue that a country's 'interest' is probably the most difficult to define, and at times, has been the central cause for needless death and loss of freedom. I would further point out, that many times, an individual or group of individuals shaped/warped/created national 'interests' that were actually not needed/warranted.
The world as it is, seems to state those countries with the largest means at its disposal are 'free' to decide what constitutes their interest. To help balance that out, we have world political/economical/diplomatic outlets. The world as it is, states plainly that those outlets are mostly useless against countries with the means at their disposal to get what they want anyway.
Before I go on, what am I missing? (keep it just to the topic at hand since I'm not talking about how we want the world to be, just yet)