The sheer amount of retardation I've seen in response to criticisms of this chapter has inspired me to go through every point which could be raised in Fujimoto's defense:

>'Denji's regressions aren't "bad writing" because they're realistic to how a victim of trauma*, abuse, etc. would act!'
*Note: The harm this word has done to discussions of psychology is comparable to 50,000 9/11s.
This is the most common response to the most common criticism of Part 2, and it's almost understandable in one respect - often in horror movies, when a character does not act perfectly logically and avoid every trap of the killer's, the audience criticizes the writing for being "dumb"; but it isn't the story that is dumb, it is the character's decision, and so long as those decisions are realistic according to their context, in conjunction with the personality of the decider, the script is fine.
With Denji, there is no use debating over how realistic his actions are because the context of his actions are far too extreme to understand: you've been orphaned, sexually assaulted a million times, killed a million times, orphaned again (RIP Nayuta), and the world is ending -- good luck. However, what we can criticize with regards to Denji's writing is his personality.
Denji effectively -- at this point in the manga -- has zero personality. He has no inner thoughts, he shows no examples of growth, he doesn't even show examples of being scarred, not anymore. His foster daughter was murdered and he's hardly even thought of her; the last woman he cared about is being controlled by the literal apocalypse and he wants to fuck the apocalypse (via her body.)