US dealers, their lobbyists and collectors insist that before asking for restrictions aiming to curb the sales of smuggled portable antiquities ("retentionists") source countries like Italy and Greece should sell the "duplicate" items in storage to collectors. The latter, as is their wont, will immediately lose all and any documentation pertaining to their origins. Here is one of those accumulations of duplicates (from the Museums Week twitter feed)
These items are in the basement and other stores of the British Museum. They are there as research and study material, for display in temporary exhibitions, for loans to other museums and other purposes. Selling them off would weaken the ability of the Museum to fulfil its functions. Why idiot collectors persist in repeating this mantra without thinking about it is anybodys guess.