It seems incredibly disingenuous to me for leftists to criticise the right's complaints about media bias as mere "whining". In American politics the media is generally seen as the referee and scorekeeper, and if they're biased in a particular direction that would appear to be a highly relevant factor in how the game is played.
So the question really is whether or not the media is biased, right? If it is, then complaints about the bias are legitimate and substantial, not mere whining. And all the evidence suggests that not only is the mainstream media incredibly tilted towards left-favorable coverage, but they know it and intend for their coverage to help "their side".