A true monist would realize that any experience of the uploaded being that received a copy of the brain is not felt by the original brain that has been copied. This is a fact and it is elementary to see it as true, as well as supporting the view that the copy is not the same being at all. If your description of computation functionalists is accurate, then they simply are dualists and would do good in admitting this to themselves.
Invoking the Ship of Theseus is a distraction. The Ship of Theseus paradox does not involve a full copy at the atomic level while the original still stands. If it did, the paradox would not even exists. The paradox exists because there is the key element that you do not have in mind copying/uploading: _continuity_.
Invoking the Ship of Theseus is a distraction. The Ship of Theseus paradox does not involve a full copy at the atomic level while the original still stands. If it did, the paradox would not even exists. The paradox exists because there is the key element that you do not have in mind copying/uploading: _continuity_.