"No one believing in Jesus commits mass murder."
-- Bill O'Reilly on Norway shooting and Christian extremist Anders Behring Breivik
If you're curious, it's called the "No True Scotsman" argumentative fallacy. It's also, even as a straightforward claim, tremendous bullshit, as a good portion of history has demonstrated.
As for the so-shameless-it's-comical hypocrisy in how an avowed Christian mass murderer is treated by these people versus how any self-described Muslim killer is -- it's really not even worth going into.
Adding: By the way, the montage of Fox News talking heads Stewart runs through -- culminating in Hannity's final, hilarious bit of punctuation -- is why The Daily Show could easily make the claim that it's got some of the most ferocious journalists in the country on its staff.