But if you don't know who is original or copy, you may start to worry about.

It seems to me that who is the original and who is the copy is irrelevant to my reaction in the leg amputation thought experiment. But, who is me and who is not me is very relevant. For example, suppose I am a copy of the original gpepper. In that case, I would be less unhappy about the original gpepper having his leg cut off than I would be about having my own leg cut off.