Some folks - even a few at Daily Kos - have suggested that Keith Olbermann, Ed Schultz and even Rachel Maddow - are opposite numbers for Beck and other right-wing commentators. It's difficult to imagine a deeper slander.
This cannot be reiterated enough. The people on the left analagous to Beck are 9-11 conspriacy theorists and the most radical members of PETA. Notice that folks of that pursuasion are not given prime-time television shows.