When media ownership is concentrated, as it is today, some of the worst consequences are: 1) Commercially driven, ultra-powerful mass market media is primarily loyal to sponsors, i.e. advertisers and government rather than to the public interest; 2) If only a few companies representing the interests of a minority elite control the public airwaves of 300 million US citizens, then calling them "public airwaves" is only lip service; and 3) Healthy, market-based competition is absent, leading to slower innovation and increased prices.
We are seeing all of these conditions today. Reasonable regulations that prevent monopolies that control what information reaches the American public, such as the ones that existed from the 1940s though the 1970s, should be put back into place.