Certainly I'd be a lot more ashamed at having my rant at the top here if not for the ability to collapse it.

And there is an aspect to that ability that I know people don't like.

The ability to collapse means you feel less bad about somewhat-off-topic conversation, which in a way can create worse discussion for the actual topic.

But at the same time some of my favorite HN threads have been offshoots of the submission's topic.