I'm a bit torn on this request of yours: I don't think people should be penalized for good-faith responses that contain wrong information (so, no flagging), but unless we're all going to spend the time to reply to and refute the wrong information, we should be downvoting those so the stuff with correct information has a better chance of floating to the top.

HN mods (or perhaps pg) have said in the past that "I disagree" is a perfectly reasonable use of the downvote button.