In 1949 the FCC introduced the Fairness Doctrine. It required all holders of broadcast licenses, both radio and television, to discuss both sides of any controversial story. This ultimately exposed viewers to a diversity of viewpoints rather than a single, narrow-minded viewpoint as we often are in today's society (see Bill O'Reilly among others).
The FCC decided to eliminate the Fairness Doctrine in 1987. This is considered by many experts as the beginning of the devolution of the American press and at least partially aided to our partisan politics of today. Canada along with many European countries still have a Fairness Doctrine.
The airwaves belong to the PUBLIC. Corporations are simply license holders. The rise of cable television does not change this equation.