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In most cases a site's "rate this comment" feature allows users to reflect on how useful, interesting, informative, etc. a comment has been for them. This is good. On the other hand, when individuals post comments that are argumentative, rude, off topic or otherwise negative, they will get negative ratings. Most people pick up on this and stop being poor posters or just get depressed and move on. Not all negative posters get the hint though. Short of disciplinary action, there's not much that can be done about such posters, and their established track record will follow them. Think of this as the result of their own actions.
You have no obligation to even notice the ratings, let alone pay any attention to them.