It's not the entire problem, but posting about politics is low-effort content. It is easy to produce and easy to consume.
It's possible to have a good political discussion, but you need really good and hard-working moderators. If HN wants to have political discussion, it would more moderation than it seems to have right now in total, but devoted entirely to that, not to anything else.
http://www.reddit.com/r/Psychonaut/comments/o1zjo/ban_memes_...
It's not the entire problem, but posting about politics is low-effort content. It is easy to produce and easy to consume.
It's possible to have a good political discussion, but you need really good and hard-working moderators. If HN wants to have political discussion, it would more moderation than it seems to have right now in total, but devoted entirely to that, not to anything else.