I recommend against deleting unpopular comments. Editing in something like "Update: I disavow!" if you've changed your mind is harmless, but in general there's a benefit to treating public statements as a sort of permanent record.

This practice exposes people to potentially underappreciated viewpoints and allows others to track the development and popularity of ideas.

I have many poorly rated comments preserved here, but on balance I think people respect my personal commitment to the truth, however I see it. In the realm of public expression, it's honesty and integrity which matter most. Everybody is wrong sometimes; it's part of the process of discovering truth.