As a "Red-diaper baby" (Communist seed) who hangs with the Communists at Pacifica Radio and other notorious nesting grounds, McPherson is hardly a bastion of anything, except maybe orthodox Marxism-Leninism. He was Clinton's heyboy historian for quick quotes supporting Clinton's social policies and politics, and he and fellow Marxist historian Eric Foner (of Columbia University, the original "little Red schoolhouse") rewrote the guidance and docenting materials for visitors to the national Military Parks like Gettysburg, to inculpate and blacken the Confederate side and their cause, because that was part of Clinton politics, which relied heavily on "booger-man" demonization of the white South and its heroes.
As you say, McPherson is hardly a champion of the old Lost Cause, but even he gets flanked by this new breed of demonizers and segregators, whose battle cry sounds a lot to me like "Crackers to the back of the bus!" And I'm from Indiana, myself.
This raises the WWWD question: what would Woodrow do? Did anyone since Lincoln more expand FedGov power? And did the Princeton President, icon of the Left, disavow the flag in question?