This part I shake my head at:

So Nick does this in the immediate need to protect his mother. He takes out Otto, but he’s going to suffer for that subsequently. One of the things we’ve always tried to do when it comes to murder is make sure that if you commit that act, that you do feel it and suffer for it subsequently.

That's pre-Apocalypse thinking. Negan, for example, needs a good murdering. Who should suffer for that. No one. I never bought that Carol would have to go into seclusion over her list of kills. It's natural to go into depression over day to day existence in a terrible world, but I don't think murder intrinsically up-ends peoples' souls in the Apocalypse. Maybe Nick will suffer because he had a relationship with Otto, but not because of some silly rule that everyone in every circumstance must suffer.