BTW, that link given by evilhanz also has one of my favorite classical pieces as background, even if that’s not a particularly good rendering of it.
What’s curious is that THIS particular piece of censorship makes the work darker and more nihilistic. They cut out a chapter where Alex renounces his amoral past, not an ultimate piece of nastiness that was just too far over the top. You find many accounts of the fact that it was cut out and what the chapter was, but not why.
My own WAG would be that an American publisher simply thought it played better with the nihilistic ending, and didn’t have enough respect for Burgess not to mess with it. This was an age when America was very taken with the idea of the antihero, after all, and traditional morality was being strongly questioned. Having a character like Alex repent might have seemed, well, a cop-out. Some critics concur that they find the final chapter weak, but that doesn’t excuse trampling on the author’s intent.
I would suggest that if the life of Christ were modern fiction somebody might, indeed, suggest that they lose the ressurection. You don’t need the story whimpering on after the logical climax. Or they’d have a fade-to-black at the empty tomb to set up the sequel.