Why is NPR so darn liberal?

In its obituary marking the death of iconic liberal activist and historian Howard Zinn, NPR allowed right-wing hater David Horowitz go off on the recently deceased: 

"There is absolutely nothing in Howard Zinn's intellectual output that is worthy of any kind of respect," Horowitz declared in the NPR story. "Zinn represents a fringe mentality which has unfortunately seduced millions of people at this point in time. So he did certainly alter the consciousness of millions of younger people for the worse."

That brought a deserved rebuke from listeners, who were encouraged by FAIR. NPR's ombudsman then looked back at how the radio network handled recent obits of other political players, who were all conservatives [emphasis added]: 

NPR was complimentary and respectful in memorializing [Bill] Buckley, who died in 2008. The network was equally nuanced in remembering pioneering televangelist Oral Roberts (who died in December) and Robert Novak, a conservative columnist who played a key role in the Valerie Plame debacle and who died last August. NPR's obituaries of these men did not contain mean-spirited, Horowitz-like comments.