Perhaps it is a good thing that you can't downvote. I'm not sure. Is being able to downvote a necessary condition to "engage"? Or does not being able to downvote force us to engage, not with an easy click, but with a considered comment?

Perhaps this condition adds to HN's value as a venue where you can expect to encounter thoughtfulness? It's why we come here after all. Or perhaps it trains the new user how to use the site in ways best suited to HN's culture?