What are good reasons to leave negative reputation?
Negative reputation should be given if the person is posting something that detracts from the conversation. If the post is rude, inappropriate, breaks forum rules, is not gracious, etc; these are all good reasons to give negative reputation. If you have a personal grudge with someone, it is not appropriate to give them negative reputation without reason. Giving negative reputation because you don’t agree with what was said is not an appropraite use of the reputation system. People are entitled to their own opinions, and just because you don’t agree doesn’t mean the user was wrong or not contributing to the conversation.