The uniqueness of a calculation matters. Running the same program twice doesn't give you a new result.

Running the program a second time is definitely an ethical violation. It would be analogous to me torturing you for an hour, wiping your memories of the past hour, and then torturing you for another hour. Alternatively, if I torture "you" in this universe, and then pop on over to the adjacent universe, it's no less of a crime for me to torture your counterpart.