Every newspaper has an editorial voice. It is acknowledged that the Post's is neoliberal, but as the OP is reporting and not editorial, it's a red herring.

The problem is that the lines between reporting and editorial are severely blurred in most publications. Just because the heading doesn't say "Opinion" or "Editorial" doesn't mean that the article isn't packed full of loaded headlines, biases, willful misinformation, and convenient leaving out of certain aspects of a story, usually driven from the top of the organization. I'd suggest reading Manufacturing Consent by Noam Chomsky for more information on the topic.

I've read Necessary Illusions; I had understood they covered pretty much the same ground, is that not the case? Anyway, all of the articles on FAIR's list were opinion pieces. If there's an analysis of its reporting of a pertinent event as compared to a less compromised source, it would help.

You proved my point. Only TWO of the articles on FAIR's list are marked as "Opinion" or "Editorial". I checked every single one on WaPo's site.

That's probably because those are the only ones that were also in the print edition. The others are blog or analysis pieces. Which, by definition, are opinion pieces. One of the section headings even includes the word blog in its name! That seems pretty clear to me.

By who's definition are blog pieces automatically opinion? That's my whole point - it's not obvious what is and what isn't an opinion piece, and your average reader is not going to know the difference or notice. Furthermore it's not like writing an article is like some closed form mathematical structure. A supposedly researched and referenced "non opinion" article is typically full of implicit opinion.