Negging content is good for self moderation. But I think it's abused by members when they neg generally inoffensive comments only because it goes against their own insulated opinions. Imagine a random passive aggressive giving you the stink-eye because you told the person next to you about your affection for Neil Diamond music. A simple "Reason" field published with the anonymous negative vote gives meaning and feedback. Also makes them reconsider if they should really be downvoting.
UPDATE
Thanks for everyone's response. I had realised that this idea was probably not going to work the way I first imagined because unfortunately with all legalities concerning published content, any comments appended onto negative's would need moderation. This wouldn't be a problem if downvoters could choose from a list of preselected reasons (instead of writing their own), and it might be possible to narrow the list down to a few options. Could even integrate an alert for moderation, e.g.
<code>
— Reason —
Rude or Offensive
Unhelpful
Other
Spam (Will alert moderator)
Abusive or Attacking (Will alert moderator)
Defamatory, Slanderous, Libellous (Will alert moderator)
</code>
Or another suggestion was to do away with the downvoting system for comments alltogther. Another suggestion was for us (and me) to move on because the topic is actually so insignificant. I'm agreeing with the latter.
The problem is that the intelligence of a mob is inversely proportional to the population. If one person negs a deal it makes it much more likely for another person to do so, even if they don't understand or cannot verify the original reason. And when there are two negs….
You are correct that this also applies to positive votes. Generally speaking however, the damage of the problem is less here.