But the important thing to understand here is that this is a choice. They could close that deficit in a heartbeat if they wanted to.
As Berkeley's Michael O'Hare puts it:
"Wait a minute .... The Met has a collection worth at least $60 billion, thousands and thousands of objects almost none of which (by object count or square feet of picture) is ever shown or ever will be. ... Selling just two percent ..., for example, could endow free admission forever. Selling .3 percent would cover that pesky deficit, also forever. ... Nothing in the Met’s mission statement suggests its purpose is to accumulate as much art as possible where no-one sees it. But the Met and all the other big art museums have insulated themselves from this sort of awkward question by writing a code of ethics that forbids any museum from selling anything except to buy more art."
(For a longer version of O'Hare's argument, see here.)
Kevin Drum of Mother Jones seconds the motion:
"The art world generally believes that deaccessioning is a horror because art is a public trust blah blah blah. This is little more than meaningless word salad. ... [I]t's hard to understand why art museums, alone among all the institutions of mankind, should be required to never sell anything they own. Perhaps this statement from the AAMD about the Delaware Art Museum's auction tells the real story: 'It is also sending a clear signal to its audiences that private support is unnecessary, since it can always sell additional items from its collection to cover its costs.' We can't have that, can we? That would prevent museums from raising money with scary campaigns about shutting down or firing half their staff or cutting hours to the bone."
Drum also predicts what would happen if the deaccessioning taboo were ditched.
"What would happen? My guess is: nothing much. Museums that gained a reputation for doing it routinely would indeed suffer a drop in private donations, and that would act as a natural brake on the practice. Other museums would benefit, as they were freed to occasionally sell off less important parts of their collection in order to pay bills or undertake other worthy endeavors. And huge museums like the Met, with caverns full of artwork that's never shown and has limited scholarly use, could not only shore up their finances but improve the world by selling pieces to smaller, more specialized museums that would show it."