As an independent collections manager/registrar, I have this fantasy/nightmare about meeting with a new private collector client, and with the ink still wet on the NDA, I greet a famously stolen object, like the Vermeer from the Isabella Stewart Gardner Museum heist, in the parlor of their Upper East Side townhouse in New York when I visit their collection for the first time. A decision confronts me: report the work and face a lawsuit for breaking my confidentiality and confidence with my client and who knows what else, versus remaining silent and, consequently, excusing the actions that led to the acquisition of the object.
The Storytellers
I have a more likely theory (maybe I should actually ask a curator why): they get recruited to those positions because they are good storytellers. They craft and relate narratives around institutions, around objects, around exhibitions that inspire curiosity and devotion among donors and earn loyalty from those around them.