I've basically been arguing here for a decade now that there can be two coherent theories on deaccessioning.
You can think it's always wrong -- that museums hold their works in the public trust, for the benefit of present and future generations, and they should never be sold.
Or you can think works can, on occasion, be sold, if there is a sufficient reason. That reason can be to acquire other work. Or it can be something else (e.g., to keep from going out of business). You have to look closely at each individual case and decide. (This is my view.)
It's the middle view -- the view of the Deaccession Police, the view of the AAMD, the conventional wisdom in the field -- that is, frankly, ridiculous. It holds that deaccessioning is deeply unethical and a violation of the public trust if the proceeds of sale are used for Purpose X (anything other than buying art) … but completely fine if the proceeds are used for Purpose Y (buying art). I've never understood how that could be at all persuasive to anyone.
Former museum director Steven Miller has a piece in The New Criterion coming at it largely from the first perspective, and calling out "the obvious hypocrisy of voicing concern for the survival of collections, only to sell them into oblivion":
"Though it is largely accepted within the profession, deaccessioning is still a controversial issue. The debate surrounding it surfaces with alarming frequency. For the most part, however, complaints are rarely directed at the practice itself, but at what happens if any profits realized from the sale of the museum collections are 'misused.' Furor tends to erupt only when income will cover operating expenses or capital and debt payments, rather than pay for future acquisitions. Oddly, controversy about commercial deaccessioning sidesteps the fact that, unless the purchase is made by another museum, objects will probably be lost to the public forever. How does that practice align with the preservation imperative museums repeatedly embrace …? Put simply: it does not."
He adds that once a work is sold, "we might as well have tossed them on a bonfire. This is a total abrogation of museological duty."
What's his answer? First, "recognize this practice for what it is and acknowledge that it contradicts a museum's commitment to preserving and caring for its collections." And then he ends up signing on to the Ellis Rule:
"Correcting the unfortunate results of unbridled commercial deaccessioning is simple. An item can be deaccessioned and kept by the museum for educational purposes. Or it can be sold or given to another museum. Everyone wins in this situation …. One museum's loss can always be another's gain."