Yes, but that argument wouldn't fly well.
The key is looking at debates among the original founders regarding secession, laws related to treason before 1861, any mention or definition of treason in the Constitution prior to April 1861, the "compact theory” of the Constitution which Southerners were relying upon, and others. Even after Lincoln appointed four new justices to the Supreme Court during the war, Chief Justice Chase knew there was zero court precedent to back that secession was treason. Zero.
They'll tell you today Confederates were traitors guilty of treason yet they had to let Davis walk based upon U. S. law prior to 1861. They'll argue they did this back then for reconciliation but the truth is the Constitution and U. S. law never made clear that secession was not permissible and especially never said secession was treason. Proof of this was several northern states saying they would secede if this or that issue was not resolved. Proof of this also lies in not one single Confederate veteran being charged with treason. Further proof of this is the 14th Amendment, Section 3 where treason was spelled out and made very clear in 1869 specifically to address the secession issue and to stop this from happening again. No law passed in 1869 or anytime goes back to actions that took place prior to that. No one goes around saying this person or that person is guilty of murder if prosecutors found that they did not have enough evidence to go forward with trial (and thus no conviction) yet some today say Jefferson Davis and Robert E. Lee were guilty of treason.