I think that NPR did themselves a disservice by firing him for this particular comment. But it wasn't about this particular comment and the news has reported that Juan has even said that. NPR has a strict ethics code that it's correspondants not make public statements that are inconsistant with their standards of reporting. So they have been "censoring" their reporters from the day they hired them. That's what any code of ethics does. It censors your freedom of public speech. It's just not been a public issue until now.
Unlike Fox and other news networks, NPR's policy is to report the news without editorializing it. And I believe that they do that. That's not to say that some people aren't going to feel they are liberal. A liberal slant could be achieved by choice of both topics and who you interview, without their reporters specifically editorializing. I'm not going to argue that point.