I think it's not so much that meta is discouraged as much as knee-jerk emotional meta reactions are, because they rarely lead to useful discussion. Complaining about downvotes or that you think the mods are being unfair are ultimately selfish actions most the time that drag the rest of the discussion down. At the same time, people sharing some of their favorite "HN discussion brought amazing person to the fore that shared" moments and links to them has allowed me and others to revisit and share in those moments and learn some of those amazing things shared even though we weren't part of that discussion.