Being the US is a little like being the small town Doctor who makes more than everyone else in town. Everyone is always watching you as they pass you the donation basket in church. They wonder "Will you give your share?" Everyone has an idea of what your share is also. They know that rich people are stingy (UN Spokespeople Love Uncle) despite what the facts say. Most of those poor opinions are based upon what the observer makes (less) and what he thinks the rich Doctor makes (expectations are often higher than reality).
So, with class, politics, race and human nature all in the mix how much should the US give?