"Anything that good hackers would find interesting. That includes more than hacking and startups. If you had to reduce it to a sentence, the answer might be: anything that gratifies one's intellectual curiosity."
I'd argue that we should simply flag accounts as hackers, thereby, by definition, greenlighting anything they post, except I wouldn't be one of them.
Do you think I should submit this link?
http://en.wikipedia.org/wiki/Isaiah_Berlin
(I read it today to satisfy my intellectual curiosity.)
It's impossible to follow the guidelines precisely, because good hackers aren't all interested in the same things. For any post outside the safety zone of, say, programming, startups, math and maybe physics, there will be some good hackers who aren't interested. But it doesn't follow that others won't like it a lot. The trouble with the "off-topic police" is that they're trying to speak for all hackers about what's not interesting. Le HN c'est moi.
Edit: How about this? Do you think I should submit it? http://online.wsj.com/article/SB121858701285435131.html