One problem with that argument is the conventional northern wisdom - backed up by an ex post facto ruling by the U.S. Supreme court - that the southern states did not secede.
No stars from the U.S. flag were ever removed signifying secession of the southern states.
Well a Southern Confederate gov’t set up and a four-year, very bloody war waged that said that the South had removed itself from and was the enemy of the USA regardless of a legal issue the Supreme Court may have had later.
Under those circumstances, I think the South’s consent was not necessary for those Post-Civil-War Reconstruction Amendments.
At first glance that seems persuasive, however, a lot of fine people fought and died under the Stars and Bars.
The Federal government at the time, while obviously asserting that the confederate states did not have the right to secede, certainly (when convenient, of course) proceeded as if they actually had seceded. Technically, for example, if these states had not seceded it would have been difficult to maintain a proper quorum in the House and Senate without the presence of southern congressmen and senators. Also, in international law, a blockade is an action that an independent nation imposed on another one - yet the US government certainly imposed a blockade on the CSA and expected other nations to honor that blockade. Finally, the Constitution prohibits the creation of new states from the territory of old onws without consent of the state legislature involved. The creation of West Virginia from Virginian territory would seem to be unconstitutional unless it were recognized that Virginia was no longer part of the USA, and hence that constitutional prohibition did not apply.