http://www.plantingpeace.org/facts.htm I already think the US is pretty great but imagine if we had spent 10% of what we spent on Iraq in the poorest countries on earth we would now be lauded the greatest country on earth by just about everyone.
I know of no laws that prevent you and those who think like you from giving all you want. What you are really saying is "why doesn't the gov't take money from Someone Else and give to a cause that you consider worthy. Thanks, we appreciate your generosity with Our money. Note 1: World opinion probably wouldn't change if people freely give money. What really makes them pee their pants with delight is when a socialist gov't Takes the money and then gives it to them. Note 2: European countries give more as a percentage than the US, but they don't give privately. When you add US private giving, we far outdo Europe. But they still bitch, because private giving doesn't count. (see note 1)
The US is fast becoming a socialist/collectivist state, the republicans and democrats are both for the most part liberal socialists. I would prefer imagining if we didnt waste the money on Iraq, bought the Oil, and repealed the income tax, slashed welfare spending to the extreme, and got corporate welfare, and religion the hell out of government.