Actually I think HN leans center. HN has no particularly inspiring agenda, it's mostly conformity to the status quo. There are extreme left and right on HN but they are usually down voted.
I see a lot of people leaning left and a lot of people leaning Libertarian. What's conspicuously absent is the religious right.
You have to express leftist sentiment, at least in public, because expressing other views is very bad for your career. And you'd be surprised how big the "public" space is for people who'd like to ruin you for thinking the wrong way.
That's true but just don't say bad things and you'll be fine - right?
Where the set of "bad things" gets bigger and bigger, and increasingly detached from reality, every year.