Comment by dredmorbius

It's not just leftists. It's polarization generally, with scale.

The mid-range views leave. The extremes remain. Often a sub / moderator bias selects for one polar extreme or another.

This is where HN's (generally) political-neutral moderator stance, maddening as it often is to both sides (see dang's many, many, many, many comments on perceived bias), seems to have largely succeeded. Neither side dominates, and the middle isn't excluded.