Well that "moral" equivalence clause pretty much depends on your view of secession.
Initially the view of historians was that the war came because of its Irrepressible nature. That is the way Seward described it in 1858. He saw it coming. While many in the South agreed that it's deep set causes made it irrepressible and many there worked long and purposefully to make the split happen. They wanted no part of a United States which would neither allow slavery to expand within this nation nor actively work to allow its spread abroad to the South.
The Revisionist view is that it was not irrepressible but was contingent upon accident, bad faith, etc. My view is definitely NOT Revisionist. I believe it was definitely irrepressible.
Moral equivalence is rejected because I do not believe the South stood for anything consistent with the writings of the Founders either as regard slavery or real Liberty. They found the former so repugnant that they blamed it on the King of England and hoped for its eventual disappearance. The Latter is impossible if it is based upon the removal of some men's liberty. It can never rise above oppression.
However, the Union stood for and protected ALL the beliefs of the Founders and proved strong enough to stand against a deadly firestorm of such force that many nations would have succumbed. It CAN rise above oppression now that the Compromise has been removed from the political body though with horrendous Fire and Blood.
TC- would you not agree that the term Revisionist is as I describe it? stand won't believe me.