In Altered Carbon a person's mind (or "DHF") can be backed up and easily transmitted to a different body, and human bodies ("sleeves") are a commodity that can be cloned and occupied by any other person's mind.
So especially the wealthy ("Meths") can treat their bodies like consumables. Not only are they effectively immortal, but the wealthiest view "sleeve death" as a sport: most people (with the exception of religious objectors) will readily give up their current body for one that is better, and prostitutes and sport fighters will endure physical humiliation and destruction that would otherwise be a crime in exchange for sleeve upgrades.
As best I can gather, "double-sleeving," or running one person's DHF simultaneously in more than one sleeve, is among the most serious crimes that can be committed. Even the interstellar government ("the Protectorate") does not double-sleeve its best soldiers or agents, which seems like an odd handicap. In the course of the first season we come across one high-level criminal named Dimi who notoriously double-sleeved himself. But even when talking to other criminals he seems defensive about having done that, insisting that his other instance is his "brother," not a copy of himself.
I can see how multi-sleeving would make it difficult to keep any story in the Altered Carbon universe from going off the rails. But other than as a plot constraint is there a reason consistent with the universe rules as to why double-sleeving would be a crime, much less one of the worst crimes a person can commit?