A Clockwork Orange is one of the few films that genuinely disturbed me, probably because I first watched it as a kid. I can watch it now without being deeply mortified, but the graphic portrayal of sex, violence, rape and human brutality still affects me. Kubrick loved to shock his audiences, loved to bring them into the dark and disturbing world of his films where he could manipulate the morality of the film's world as he pleased. His films meld intelligent social and political commentary with provocative visual cues: the brutal beating of a woman with an oversized ceramic dildo (a brilliant visualization of sexual violence that sticks in your memory for its symbolism and raw destructive force); Alex's slow motion suppression of the droogs' mutiny; the fast motion threesome to the tune of the William Tell Overture. Brilliant, brilliant, brilliant.
The film's atmospheric darkness is unwavering in its committed depiction of sexual perversion, social deviancy and extreme violence, and Kubrick wants it to be visceral. He wants you to cringe at the rape scenes, he wants you to feel uncomfortable. It is helped along by a score composed of classical pieces and synth-heavy reinterpretations of classical motifs, a modern perversion of a classical medium which contributes to the film's unsettling quality.
There's no reason for Alex's sociopathic tendencies; he is simply a product of a society in which people are increasingly isolated and trend toward violence, and you can draw whatever parallels you'd like with contemporary society. Obviously, and ironically, once Alex is deprived of his violence he is preyed upon by the very world he victimized so callously; forgiveness is not a very popular concept in this world and maybe the only thing people have left is their violence. The coldness of the world in A Clockwork Orange is very deliberate, and in many ways the feeling that the entire world is beyond moral redemption is just as disturbing as the actual depiction of violence. Kubrick constructs a world where there is no sanctity, where human warmth is the staple of a bygone era, and it's chilling.
I prefer the film's ending as well; having Alex "outgrow" his violent nature would have been a little too conveniently symmetrical. Plus, this way, you are left with a very memorable and lasting closing image.