I think we're running into (or at least pretty close to) a Two Guys Fallacy here:

There's still a strong libertarian streak in HN posters, in a variety of ways.

However, there are also (mostly) different posters who have more vocally shifted the site's Overton window to the left.

These days, I find it fairly common to, for instance, make a comment that points out the very obvious problems the Republican Party has created in recent years, get downvoted to -3, and then upvoted to +5 (or vice versa), all within a few hours. This would suggest that there are contingents of posters (or at least voters!) in both camps.