My thoughts on it: you can find humor anywhere on the internet. It's much harder to find decent discussion. When humor and decent discussion try to coexist, humor tends to crowd out the discussion.

Why bother posting detailed information about what kind of reaction is going on when you can make a simple joke about nuclear power and get as much karma? Why bother posting something intelligent when it will be buried below puns?

I used to think HN downvoting humor was bad, but I've really come to agree with it after looking at some attempts at serious discussion on reddit. Without fail, by the third comment or so, someone will derail it with a predictable joke or pun. Humor is easy. Interesting comments are not.

Cannot upvote enough.

That part of HN is already worse than Reddit, though.

Yeah, injecting a little humor into the discussion around here would really ruin the place.

Edited to add: may you dour bastards choke on something.