I think sarcasm is more of a problem on HN than lame humor is. Humor doesn't always succeed, but at least it's intended to make others feel good. (Think "good humor".) Sarcasm is only marginally related to humor. It's really about scorn.
Sarcasm is verbal bile. It feels good to let it out, but it acidifies the environment. It feels like you're being smart, but usually is more of a tic, like eye-rolling. A community with high sarcasm levels is like a room full of eye-rollers—not a great place for conversation. I think that's why you correctly identify it as a dead end.