In my opinion there are a lot of negatives in watching just one news source. Indeed, I feel if I watch, listen, or read to only mainstream news media there's a lot of news I'm not receiving.

From what I've experienced, Fox is heavily biased towards the republican side of the argument, but then I've seen some examples on Fox that would not necessarily indicate a total bias.

Much of the news, mainstream or otherwise, seems heavily opinionated. I'd prefer to just have the facts and be allowed to form my own opinion.

Also, there's an awful lot of news that I feel is under reported or not reported at all. But then, this is my personal bias, which if I had control of the media, would be reflected in the reporting on that media.

jaaaman's solution would seem to be one alternative.