But with a clear cut system like the one mentioned above, why shouldn't new members get to downvote as well? The system would clearly convey its intended usage, and in the process bring new members up to speed faster. If you still want to impose a restriction, it definitely shouldn't be karma based.
I find it a bit counter-intuitive. [Assume maximum evil] You're going to allow someone to downvote others based on how quickly and effectively he can troll the hivemind to give him 500-1000 or heck even 5000 karma?
"New" members shouldn't downvote because they might not downvote the right things, or for the right reasons. I do not consider lurkers "new members."
I also disagree with the idea of karma-driven downvote system. However, I wrote the above with the assumption that those who can downvote know HN values and enforce them. As you pointed out, yes the karma-downvote thing doesn't quite accomplish it's goal (assuming the goal is to allow senior members to act as enforcers). It should change. However that wasn't quite the point of my post.
My original point is: if you gonna say smack, gimme a damn good reason why.
Ah yes. You've got a good point. I find it confusing on how to allow downvotes then. Is age of the account a fair measure? Then what about people who've been here without registering, or people who actually have good discretion.
Maybe enforce a stealth downvote. This would be a case where the downvote button is visible but you use heuristics and probabilistic models to determine to whether actually accept the guys' vote or not, and if yes, what weight to assign it.