I agree the potential for damage is much higher with downvotes, but there's an asymmetry there.
The trick is to make downvotes cost a little bit of karma, IMO. And while I'm on the topic, upvotes shouldn't be as free as they are, either.
Having said that, the 2-1 downvote scheme you proposed does put some of us within spitting distance of taking nickb down to zero, so I support it wholeheartedly.
Having a secret cabal of editors, whose behavior and rules are not documented, is simpler than spending karma to vote against things? Really?