There is a book titled Shadow Divers (I would recommend) that goes into this a bit. The book tells the story of wreck divers who find a U-boat not far from New

There is a book titled Shadow Divers (I would recommend) that goes into this a bit. The book tells the story of wreck divers who find a U-boat not far from New Jersey. The story echos your friend's concern. Wreck divers will remove anything they can from these sunken vessels; placards, insignia, gauges, etc. They will also damage the vessel in order to make room to continue exploring. The German government was also not happy with the book's protagonists because they deem sunken vessels as graves and believe they should remain undisturbed.