On the legal side, I think he's mistaken. He argues:
"The Michigan AG has declared that 'the art collection is held in charitable trust for the people of Michigan and cannot be sold for purposes other than the acquisition of art'. That’s pretty unambiguous, legally."
I don't think that's right. It's an unambiguous statement of the AG's view of the law, but the AG doesn't get to make the law. Think, to mention another high-profile art law case, of the Barnes. The Pennsylvania AG thought the move to Philadelphia was okay. But that didn't mean it was okay; that was for Judge Ott to decide. Or, in a case going the other way, the Tennessee AG was pretty unambiguous that the Fisk collection should not go to Crystal Bridges. But the collection is going to Crystal Bridges.
In fact, Salmon's reasoning here is perfectly circular: "the Michigan attorney general is absolutely right that the art collection of the Detroit Institute of Arts cannot be sold to satisfy the city’s financial obligations ... [because] ... [t]he Michigan AG has declared that 'the art collection is held in charitable trust for the people of Michigan and cannot be sold for purposes other than the acquisition of art'." Nice work if you can get it!
On the normative side, I don't really take issue with anything he says. He points out that, in return for a sale, the city "would get — well, nothing, really: all the proceeds would end up being pocketed by the insurance companies which wrapped Detroit’s municipal bonds." If that's the case, then, yeah, a sale doesn't look too attractive. But that's exactly how the argument has to go. What will the world look like if the art isn't sold and what will it look like if it is sold and which do we prefer? Will the money end up pocketed by insurance companies? Or will it fix the broken streetlights, or employ more police and firefighters, or save pension and health benefits of municipal retirees? I've never argued for a deaccessioning, in Detroit's case or any other. All I've called for is a weighing of the relevant costs and benefits of each potential sale, just as museums do every day of the week when they