Did the amendment CRIMINALIZE their actions? Yep. Ex post facto. With a penalty that was not enumerated previously by law? Ex post facto. It's not hard to comprehend.
As far as some provisions of the 14th Amendment being, in essence, a bill of attainder (legislative punishment) - that is quite true.
And Bills of Attainder are STILL unconstitutional.
... at least 2/3rds of each house of Congress approved and at least 3/4ths of the States ratified the Amendment.
Wrong. In submitting the resolution for the amendment, 28 Senators had been unlawfully excluded from the Senate in violation of Article I §3 and Article V. 42 Representatives were similarly denied seats. 15 of the 37 states rejected the Amendment.
True, with the sole exception for those who, having been under oath to support the Constitution of the United States, gave aid or comfort to the enemies of the United States, or participated in insurrection or rebellion against them.
"In submitting the resolution for the amendment, 28 Senators had been unlawfully excluded from the Senate in violation of Article I §3 and Article V. 42 Representatives were similarly denied seats. 15 of the 37 states rejected the Amendment."
Each house of Congress, as I'm sure you know, is the sole judge of its membership. There is no appeal to that decision, and therefore, no lawful claim can be made otherwise. This confederate mythology about the 14th Amendment has been thoroughly refuted.
"Did the amendment CRIMINALIZE their actions?"
The traitors actions were criminal in their own right. The 14th Amendment provided a disability for their treasonable conduct. The amnesties offered by Presidents Lincoln and Johnson had saved more than a few of them from the hangman's noose.
"It's not hard to comprehend."
What is not hard to understand, except for the exceptionally stubborn or the willfully ignorant, is that NO constitutional amendment is itself, unconstitutional. When proposed and ratified, it works to change the terms of the existing Constitution and Amendments, absolutely. That's why the process is exceptionally cumbersome.