As I see it, Stewart feels that leftwing ideology is sensible, rational and correct. If the NYT is Liberal and promotes things that are sensible, rational and correct, then they are not being "activist", they are simply being good journalists. Just telling it like it is.
Now, Fox, you see, embraces a crazy, stupid, irrational and hate-filled agenda. I mean, that's obvious, right? So, when Fox pushes that sort of ideology, they are being "activist" because they are trying to push ideas which normal people know to be incorrect. Right?
In Stewart's view of the world, this is just very obvious.
Heh, good contextual explanation.
Basically, to crazy people (or, “Insane” as he puts it) crazy things are normal.
To people like him, The NYT, Sotomayor, Kagan and Ginsberg are middle of the road, and Scalia and Thomas are far right-wingers.
He REALLY believes the NYT is middle of the road.