I had what is called 'source amnesia' which is a very common psychological phenomenon where you remember a thing but you don't remember that it came from a disreputable/fictional source; this is why it is dangerous for Fox News to exist, because in time people will forget that they learned something from a disingenuous, morally bankrupt source, and ascribe to that fact more authority than it deserves...
Source amnesia also explains why urban legends spread and why people are so convinced of their factuality: you hear a tall tale from a friend and then forget that it was from your pal you heard it and assume it came from a proper source such as the news. Thus convinced of its accuracy, you go on to spread it to other people.
While I've seen this a few times on the left (mainly on the issues of gun control and the accuracy of the Lancet's Iraqi casualty report), I've noticed that this affliction seems to be running rampant on the right, and I think that Jonny's 100% right when it comes to conservative media outlets' reliance on (and exploitation of) this psychological blind spot. From a study regarding the Iraq war:
A new study based on a series of seven US polls conducted from January through September of this year reveals that before and after the Iraq war, a majority of Americans have had significant misperceptions and these are highly related to support for the war in Iraq.
The polling, conducted by the Program on International Policy (PIPA) at the University of Maryland and Knowledge Networks, also reveals that the frequency of these misperceptions varies significantly according to individuals' primary source of news. Those who primarily watch Fox News are significantly more likely to have misperceptions, while those who primarily listen to NPR or watch PBS are significantly less likely.