The liberal media is a myth that's primarily used to further a culture of perpetual victimhood on the right. While it's been a long time since I saw this interview, I'm pretty sure that Jon Stewart specifically mentions this victimhood campaign.
A liberal media myth busting article among hundreds via google targeting talk radio, which is one of, if not the most influential political media outlets:
http://www.completecampaigns.com/article.asp?articleid=88
And besides, while the Repubs were leaning further and further right since Reagan took office, everybody else pretty much remained status quo in their political views. This rather steep transition the Repubs went through is now affecting how they view themselves and where they stand in comparison to everyone else. So it's pretty logical to assume that since the Repubs have veered far to the right, to them everyone else seems poisonously liberal, including the media, when in fact it's only the Repubs that have changed so much. This recent pull to the far right has required them to also redefine what the current definition of being conservative AND being liberal is.
Witness how moderate Repubs were replaced enmasse with far right leaning legislators in recently held State/Federal elections as an example.
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