From a defense stand-point, you are probably correct.
If you look at the multiple billions of dollars the USA has poured into Africa for food and drought relief and the tens of billions the USA writes off in debt incurred by poor, highly indebted countries...as do G8 countries and others, there must be a mutual benefit, to some degree.
Of course, there are millions of dollars for poverty or disaster reasons sent out of compassion by individuals, churches and non-profit groups where the US government does not get involved. The USA is still governed and supported by humans with compassion. Unfortunately, Slomo, your point is well-taken, and "what's in it for us" is typically in the mix politically, but...giving to the poor out of love for others is still a principle taught and practiced here, from the roots-up.