> The solution is also pretty obvious: randomly review downvoted comments and if they are downvoted for disagreement and not merrit, ban the people who downvoted it from future voting. For new users shadow the votes for a while to be sure they understand the community[0].

Even if you could objectively review that, HN doesn't have a rule against downvoting for disagreement, pg decided it was acceptable very early on and it hasn't been changed. (although plenty people think it should)