We used to moderate comments posted by our visitors because some smarter Spam comment do go through on and off even thought we have Akismet installed. We never have an issue with negative or positive comments (in fact, how is this defined, we don’t know)
1. Never underestimate your visitors. They are able to tell what is genuine and what is not. Sabotage comment has shorter life span now!
2. Suppressing what not favor you will only get more of them coming to you. To block the, solve the problem immediately.
3. Your commitment to solve the problem in a more transparent way can turn those so-called negative one into positive.
4. We tend NOT to question about the genuineness of those so-called positive comments because it favors the site owner. Again, smarter visitor can tell!
5. For those positive comments which get their way out from moderation, they will not survive long because it is exposed and second wave of moderation can come from anyone not the owner.
6. In long run (as long as the Blog is active or not turned down by some authority), the comment will be neutralized
No such thing as negative or positive comment!