Why foreign aid helps US
Foreign aid is more than justifiable on humanitarian grounds alone. But whether or not the current administration realizes it, it's a powerful diplomatic tool for advancing our purposes and protecting our interests all over the world. If we'd stayed as financially involved in the well-being of Afghanistan as we were when we were quietly helping the Muhajadeen fight the Soviets, we might not be fighting many of the same people now we were helping back them.
More than that, it creates markets for American goods in other countries and helps them to develop. American foreign aid is good for American business.
Becoming miserly about foreign aid isn't just short-sighted. It's foolish. Consider: what might happen, for example, if instead of wasting all that money on a border wall which as a practical matter it will be impossible to build on the scale the president talks about, we used it to decrease the motivation of Mexicans to leave Mexico in the first place!