Although the FDA banned the use of antibiotics for growth promotion in animals, growers are still allowed to administer the drugs prophylactically- before any animals are sick. This means that growers are still essentially free to use as much antibiotic as they like on their animals, which helps the spread of antibiotic resistant bacteria.
Another possible harm is that exposure to the antibiotics that remain in the meat might affect the bacteria normally resident in our bodies. While this is still somewhat speculative, it's worth looking into....