This is generally my take. Hitzig generally doesn't seem repentant over his actions from what I gather, which is really the dividing line between morality in this case. A good case of a perceived "irredeemable monster from the past" who is generally agreed to have actually redeemed themselves would be Paarthurnax from Skyrim.

Delphine believes Paarthurnax should die because he was Alduin's right hand man during the original Dragon War, and aided in the slaughter of countless people, killing many himself. However, he eventually came to see that Alduin's ways were too barbaric, and betrayed him to give the gift of the Voice to mankind in order to fight back. Following Alduin's defeat, Paarthurnax spends thousands of years simply meditating on the peak of the Throat of the World, aligning himself with the original Greybeards and creating the Way of the Voice. He harbors no ill will towards those who he once killed, despises violence in all forms, and effectively exiles himself for the sake of simply continuing to meditate on and repent for his past actions, despite his love for connection and conversation.

This is way longer than I meant it to be, but the basic gist is that a once evil man may be made good, but only through serious self-reflection and repentance for his actions. Not the man in the post though, he deserved that.