More accurately, NPR reports on topics of interest to a broad swath of consumers in a factual and thorough way, without making pains to appeal to the emotions of a specific subgroup. That this method of journalism does not well-align itself with conservatives, Republicans, or their agendas is not an indictment of NPR's supposed biases. Rather, it is a reflection of just how insulated from the facts and others' viewpoints some groups of media consumers have become.
And guests of their shows frequently express leanings toward or away from specific ideologies, both left and right. While the guests may be pressed in ways that make them uncomfortable, in no way are they intentionally offended or denigrated by the hosts.
The firing of Juan Williams was a gaffe. While I do agree that some statements he had made did make it difficult to see him as a credible and objective reporter on some topics, I do not think that it is correct to fire a journalist or any employee for personal viewpoints unless they are expressed in such a way as to be harmful or disruptive to the business.