The US doesn't import corn from South Africa, but, in any event, "Corn fit for human consumption" is not co-mingled with corn sold as ethanol feedstock.
Maybe 10-12% of the US corn crop is consumed in some form by humans, the vast majority of this is in the form of high-fructose corn syrup, with a minor portion in the form of food such as corn chips, tortillas or canned corn. Almost of of this corn is "white" vs. "yellow" corn. Corn intended to be used as human food in the US is grown on direct contract with the food processor because of quality control, genetic and other concerns.
Well well. Your “#2 yellow corn isn’t used for human food anyway” is not 0% but 10-12%.
I suspect that even that number is just direct consumption, not indirect.
For example, if any of it is used for feedstock, that is for human consumption as well, isn’t it?
We are also talking about humans in a worldwide sense, not just humans here in US.
The humans outside the US are the ones most susceptible to starvation and in need of food, regardless of whether it meets all the specs the USDA places on us for consumption here.