Aesthetes always bend to the right, in part because the best music and the best buildings were made in the past, and become an argument for its qualities. Someone entering Chartres becomes, for a moment, a medieval Catholic, and a person looking at Bellini or Titian has to admit that an unequal society can make unequalled pictures. To love old art is to honor old arrangements.
An arguable point at best, particularly given that Mill was steeped nearly from the cradle in the wisdom of the ancients, and, well, Plato was hardly a liberal. There may be some truth in the notion that art can scramble and complicate political allegiances, and that in some sense an aesthetic view of the world leaves us open--sometimes dangerously but almost always to our benefit--to seeing things differently, and appreciating the complicated humanity of people we might otherwise think we should deplore, from Wagner to Waugh.
To his credit, Gopnik's next statement is stark, similarly provocative yet harder to dispute:
But even new and progressive art is, as Mill knew, a product of imagination and inspiration, not of fair dealing and transparent processes; the central concerns of liberalism—fairness, equity, individual rights—really don’t enter into it. Mozart, whom Mill loved, would have benefitted as a person had he lived in a world that gave him the right to vote for his congressman, collect an old-age pension, and write letters to the editor on general subjects, and that gave his older sister her chance at composing, too. But not a note of his music would have been any better.
The real thorny (not to mention unanswerable) question is not how good or bad Mozart's music would have been given a freer social milieu, but whether Mozart would have written a note of it if he lived in, say, the Victorian era, or our own.