He's a total ignoramus in that regard. Over grazing has damaged enormous areas in the arid West, leading to reduced productivity in a self defeating downward spiral for ranchers. Over grazed, lands that once could support one cow on 20 acres support only one cow on 40 acres, then 80 acres, eventually become barren or nearly so.
WRT public lands, it's called the tragedy of the commons-
http://en.wikipedia.org/wiki/Tragedy_of_the_commons
It's what happened over much of the middle east & the mediterranean, also China, occurring over hundreds & thousands of years. Primitive herders & farmers didn't know what they were doing because it happens slowly over generations. We do know. In that, we have an obligation to provide good stewardship of the land for future generations.