Earlier quoted context omitted.
Comments to most articles about Snowden, refugees or gender issues are like that.
Probably a signal that the user base does not find those issues interesting. Snowden because it's nothing we don't already know, and refugees or gender politics because they always degenerate into political (i.e. not interesting) mud slinging matches. On a side note, if a community with the general high quality and good moderation of HN can't have a good discussion on those topics online, I'm inclined to believe that…
Marking down the comments indicates a desire by some to to enforce groupthink. Why? Because many people use votes to indicate agree-disagree instead of a quality metric.