First off,the homeless population is nowhere near what some think it is. Those that are homeless have plenty of places to go in this country to get help. There are plenty of gov't supported welfare programs as well as many not-for-profit organizations to assist. In a country of 280 million, there are bound to be stragglers, unlucky & bums. Nobody goes hungry in America, if they do something to avoid it.
Secondly, in a country that is as rich and prosperous as ours, a little charity to assist those in countries where they can't help themselves is a matter of national security. It's a hell of a lot cheaper to help Russia than to spend 40 years in a cold war. Same goes for China, with over a billion in population. The countries that aren't close to equaling us in military might still have terrorists & dictators that can set a fire somewhere else to get us involved. Look at Palestine. Yassir is a complete & udder nobody, but look at the trouble he has made for the US, just with our support of Israel.
Personally I'd prefer to send money bags that come back empty than send bodies that come back in a bag.