Noted: W.E.B. Du Bois
From Du Bois' monumental and essential Black Reconstruction in America, 1860-1880:
The discussion which has raged round the Reconstruction legislation is of the same metaphysical stripe characterizing all fetich-worship of the Constitution. If one means by "constitutional" something provided for in that instrument or foreseen by its authors or reasonably implicit in its words, then the Reconstruction Acts were undoubtedly unconstitutional; and so, for that matter, was the Civil War. In fact, the main measure of government during 1861-1870 were "unconstitutional." The only action possibly contemplated by the authors of the Constitution was secession; that action, the constitutional fathers feared and deprecated, but their instrument did not forbid it and distinctly implied the legality of a state withdrawing from the "more perfect union."
Certainly no one could argue that the founders contemplated civil war to preserve the Union or that the Constitution was a pro-slavery document. Yet, unconstitutionally, the South made it a pro-slavery document and unconstitutionally the North prevented the destruction of the Union on account of slavery; and after the war revolutionary measures rebuilt what revolution had disrupted, and formed a new United States on a basis broader than the old Constitution and different from its original conception.
And why not? No more idiotic program could be laid down than to require a people to follow a written rule of government 90 years old, if that rule had been definitely broken in order to preserve the unity of government and to destroy an economic anachronism. In such a crisis legalists may insist that consistency with precedent is more important than firm and far-sighted rebuilding. But manifestly, it is not.