I don't think he was wrong.
When people like him think the way that they think and have been through whatever they have experienced..is understandable for why and how he did what he did.
In his position, I agree with everything he did. Including the fact that he did NOT pick Shiori. People like her will never change the mind of a person like him. Yes, Naruse did rethink what he was doing, and yes he most likley had deep feelings towards her..but when you're in a situation like that ..and you are loosing control of your actions.. which one would you pick? After all of what you have done, and planned? Naruse is a man of his word.
I also agree to the fact of the revenge he was seeking. It is understandable that he was hurt and that everyone close to him have died, no one was left for him..Thus, he began to plan and take action. I think that it was a big slap in the face to Naoto when Naruse killed or plotted against everyone that was close to Naoto. To feel the suffering that Naruse felt for 11 years. Although.. it is true that Naoto suffered from the fact that he killed someone as well. Naoto also disliked the fact that he killed Naruse's brother, but in the end, who would believe that it was an accident with no proof? With the background that Naoto had. [Being a bully and such.]
Naruse was a mastermind. I loved the fact that he wanted to die at the end as well, because in his eyes he was a monster, and he couldn't live any longer and couldn't go back after all of what he had done. Naruse had taken the risk, and decided it was too late to make any sudden arrangements.
Maou was a great drama, definatley 10/10.