it does come off as a bit one sided becuase the implication is that when you say "progressives do this" you are also implying that non-progressives don't--even if its not explicit. As someone who sits squarely in the middle, I see this heavily on both sides. A better formulation would be "partisans aren't known for wanting to be neutral or muted about their causes." If they had hired more conservative journalists they'd have the exact ssame issue but in the opposite direction.

(full disclosure--I haven't watched CNN or any other new channel since the Iraq war, i.e. 19 years ago. The all burned their bridges with me then, and I've never been back, so I'm assuming its true that CNN has a tilt left. I've never seen it myself.)