Plagiarism - I think a lot of people would argue that this is a moderation issue and not something that members should be taking into their own hands. Simply report and the user will get banned and that's a far more effective way than leaving a tag because its permanent and actually achieves something.
Ban Evasion - Again for the same reason as Plagiarism.
I didn't mention harassment in my system. Misquote?
Sometimes users plagiarize/ban evade and moderation is slow. We know how slow moderation is. It seems better to at least "soft-ban" these users first.