With how, even after, SPOILERS, he came to realize it was him who hurt, violated and possibly was indirectly or otherwise responsible for the death of his wife, he was all like "My poor boy, another victim of modern age" - obviously showing his disdain towards the "Ludovico treatment" that he received but he was still mad and angry enough at him to play that tune gleefully and then almost drive him to suicide towards the end?
So he essentially both sympathized with Alex AND hated him, correct?
And that scene also had a surreal and darkly humorous vibe to it, I bet loads of filmmakers later like David Lynch, Peter Greenaway, Harmony Korine etc etc got some inspiration from it, as well as this film in general.
P.S. On a side note, its interesting how only once in the whole movie, and by Mr Alexander and in this scene to boot, was the word "rape" even used, throughout the whole movie, it is mostly referred to or alluded to as either "the old in out" (although it also refers to instances of consensual sexual activity in this film too, which we do see as well), "old ultraviolence" (but then, does "ultraviolence" only or even MOSTLY refer to sexual violence in this film or violence, physical, in general, that we ALSO do see) and "sex and violence" etc, and I wonder if this was in any way intentional or incidental? And yeah, its all understood of course, but possible to debate without fury OR controversy too much, like other forms of violence, perhaps?
Based on his reactions, I bet he'll probably be an avid opponent of the death penalty too, but what if Alex, someone who caused harm to him and someone close to him, was about to have it, would he be eager to defend him?
I don't agree that Mr. Alexander had any sympathy for Alex. He was just saying that to lull him into a false sense of security. He wanted to make him feel safe and lets him take a bath upstairs during which Alex makes the mistake of singing Singin' in the Rain. If there was any doubt in Mr. Alexander's mind as to the identity of the desperate man at his door, that was putto rest when he heard those fateful bars.
He then calls that politician and wife who clearly have an agenda contrary to the 'new order'. They do not believe in the Ludovico Treatment. The current government sees the Ludovico Treatment as a quick and easy solution to violent crime and recidivism. The politician, his wife, and Mr. Alexander exploit Alex by driving him insane enough to try and kill himself. The politician and his wife do it for social/political purposes. They are using Alex as a pawn to try to show just how extreme the Ludovico Treatment is and that turning criminals into 'clockwork oranges' is no solution. Mr. Alexander's motives are different. He simply wants Alex dead because he believes (and may well be correct) that Alex's brutality toward his wife led to her death.