Cheap food for the world courtesy of American taxpayers sounds like a good thing.
Unless you're a farm worker. Doesn't matter if foreign food is cheap if a large enough part of your population relies on farming that the cost savings would result in mass unemployment.
If international trade was harmful, people wouldn't engage in it.
Are the farmers in those poor countries welcoming and throwing parties for cheap fed subsidized US crops and food? What's good for some isn't good for all.