Although I think that there absolutely needs to be a clear and set guide for when to "upvote" and when to "downvote" content, I highly doubt its going to stop everyone from carelessly downvoting something they dislike, etc. It's impossible to enforce a system that is inherently designed to protect the end user's privacy (which in my opinion something that is extremely important). I think the best way to approach this matter is to allow for breakage, meaning that its normal to expect a certain amount of "downvotes" to happen just because the people on here are human and they are predisposed to doing so.
As for your questions, I'm going to take a little time and let it all sink in before I give my opinion. You asked an extremely important question, and I don't want to screw it up by giving you "lackluster" feedback.