The carnist claims that agricultural byproducts are used to feed animals, not food that humans eat.
Why are people paying money to feed 80% of the world's soy to animals when they could get the otherwise useless husks of human food to feed them? Why can we feed 800 million people from the grain in this country alone, but then have people starving? It doesn't make any sense.
It doesn't matter what you feed a caged animal that you then slaughter, this act is inherently immoral, and even if it were true that it is more ecologically sustainable, that would not justify it.