@extramsg, did you even watch the video? Maher addresses this explicitly.

First, there's a qualitative difference between the strident criticism folks like Maher make and Glenn Beck's ranting. Maher's rhetoric could fairly be described as impolite and disrespectful. Beck regularly claims Obama is guilty of "treason", a capital offense, and concocts elaborate conspiracy theories that claim Americans are being sold into slavery. [citations provided upon request]

Further, Beck has an audience many times larger than Maher's. To find someone similarly unhinged on the left, you'll have to listen to late night Air America or go to Daily Kos. To find someone crazier than Beck on the right, you can look at Representative Bachmann, or Sharron Angle (who was pretty close to unseating the Senate Majority Leader).

You can't even compare the two.