You've got it backwards - foreign aid using US grown crops provides increased very stable demand. Take any excess grains made in a given year and ship them to another country, the farmers get paid well for it so they keep their productive capacity high, and the marginal cost of getting it to a charity overseas is low anyway. This means there's always enough grain to feed our citizens.

And it keeps foreign countries dependent on us and gives us another avenue to coerce them. Wins for us all around.