More Than the Sum of His Parts

Haldeman, Joe, "More Than the Sum of His Parts." Playboy Magazine and Lightspeed Magazine May 1985, as of January 2020, available at linked note.[1]

Summarized on Variety SF[2]: " A serious accident victim is saved by transforming him into a cyborg. He begins to like the new body parts. Then he starts enjoying his new found power too much, & quickly becomes a monster. [...]"

So, cyborgization story, featuring prosthetics in the world of 2058, for which cf. and contrast such stories as F. Pohl's Man Plus and D. Knight's "Masks." Also deals with theme of machine takeover, as the cyborg prosthetics arguably "take over" the protagonist, and the protagonists intends with his super-powers to take over a lot: note protagonist's journal entry, late in the narrative,

A psychiatrist, talking from Earth, tried to convince me of the error of my ways. He said that the dreadful trauma had “obviously” unhinged me, and the cyborg augmentation, far from affecting [i.e., effecting] a cure, had made my mental derangement worse. [...]

I did take time to explain the fundamental errors in his way of thinking. He felt that I had quite literally lost my identity by losing my face and genitalia, and that I was at bottom a “good” person whose essential humanity had been perverted by physical and existential estrangement. Totally wrong. By his terms, what I actually am is an “evil” person whose true nature was revealed to himself by the lucky accident that released him from existential propinquity with the common herd.

And “evil” is the accurate word, not maladjusted or amoral or even criminal. I am as evil by human standards as a human is evil by the standards of an animal raised for food, and the analogy is accurate. I will sacrifice humans not only for any survival but for comfort, curiosity, or entertainment. I will allow to live anyone who doesn’t bother me, and reward generously those who help."

Decorously for the Playboy venue, deals seriously with issues of male sexuality, and not just in terms of any Freudian "castration anxiety."