Glenn Beck is just the craziest of a fairly large selection of cable hosts.  Yes, he is significantly crazier (and almost certainly more dangerous) than most of them), but Lou Dobbs, Bill O'Reilly, Chris Mathews often, Jim Cramer, Sean Hannity, Nancy Grace, Rick Sanchez?  All crazy.  And most of the ones who are not are either overstuffed with arrogance (Joe Scarborough, Keith Olbermann, Larry Kudlow, Neil Cavuto) or utterly ineffectual as journalists (Anderson Cooper, Wolf Blitzer, Greta Van Sustern, David Schuster, Maria Bartiromo.)  But I digress.  The point is that craziness both reaches niches and also evokes publicity and curiosity.  FOX is ecstatic that this psychotic recovering addict McCarthyite that they scooped up from CNN has increased their ratings over a host (John Gibson) who merely urged white parents to have more babies to counter the coming Mexican takeover of the country.  They LOVE for him to be way over the top--UPS aside (they just dropped O'Reilly), almost any sponsor who is still with FOX is not going to drop out regardless of what Beck says, and a bunch of Conservative apologists who run FOX are not about to disagree with, let alone censure, Beck's voice.
Which gets to the true heart of the matter;  Beck is not that much crazier than the mainstream Conservative base today.  And the gap continues to narrow, and not because he is becoming more reasonable.