Media Ownership: What are the problems with 'big media'?

Free Press is a company that is building a "powerful nationwide movement" to change the current policies in media and technology, promote the interests of the public and strengthen democracy. Free Press are advocates for universal and affordable internet access and believe in diverse media ownership, high quality journalism and "vibrant public media".
Free Press believes that the consolidation of media ownership into six media conglomerates has led to corporate control over near enough all media; broadcasting stations, the internet and the print media.
Free Press want a competitive media landscape; they believe that the more independent media outlets a community has, the more diverse messages will be shared.
Ultimately, an oligopoly like this leads to stagnation in the marketplace, with a set of core values and messages consistently being sent out to an audience, with very little variation.