Was wondering the same thing, and so far I only have two half-assed explanations. The first is that Fassbender's character kept talking about "forbidding empathy" throughout, but then by letting the guy live he kind of sort of expressed empathy in the end? Thus going from "one of the few" in the beginning to "one of the many" in the end? Granted, that's not an explanation, but more of an evolution, and one that doesn't feel very Fincher-esque. The only other thing I can think of is that it has something to with all the gig economy/capitalism stuff throughout. From WeWork to Airbnb to McDonald's to Amazon to Ace Hardware to the Equinox knockoff, etc, etc, there were so many corporate brands throughout, while Fassbender's character was "an atomized digital nomad, conversant in grindset and Gladwellspeak" (a line I pulled from a review). So the "final boss" being a techy billionaire hedge fund d*uche - the type of guy who's essentially responsible for the world we/Fassbender's character inhabits/depends on - felt very intentional in that sense. And maybe Fassbender's character either realized what he thought was the necessity in there being sh*tty ruthless billionaires at the top, or the pointlessness in killing him? I don't know, something along those lines? While I loved the overall look, vibe, story, etc, I was going to do the same and revisit a few scenes on Netflix, in search of an explanation, and I have a feeling when I do I'll have an even better appreciation for what Fincher was going for.