It's not greed, just survival. For some unknown reason antibiotics have a synergistic growth effect on animals that are not sick so antibiotics are feed to healthy animals. In the real world most businesses are barely profitable so any action that can increase profits is used to avoid bankruptcy.
With population pressures and increasing antibiotic resistant bacteria our whole food producing system may have to be overhauled. This aside from the massive carbon dioxide emissions from modern agriculture that must be addressed.
In many ways Capitalism is destroying the Earth and with all of us dependent on a healthy world more socialism will be needed. As a Conservative Republican this pains me but our very survival depends on this. Instituting this without concentration camps and killing fields will be difficult.