Here's my reply, after some reflection. The reason I strive for having no comments with negative scores is so that when people see a comment from me that is confusing, controversial or just seems wrong (of course I try to prevent that if possible, but sometimes it isn't), they'll think "It's not like Wei to write nonsense. Maybe I should think about this again" instead of just dismissing it. That kind of power seems worth the effort to me. (Except that it hasn't been working well recently, hence the frustration.)