The film is not easy to watch because of its graphic scenes and strange language (Burgess created a new language for his book, which mixes British slang and Russian vocabulary and Kubrick stayed faithful to that). But once you get accustomed to Kubrick’s vision for the adaptation you realize the movie is a morality tale on crime and punishment.
Alex is the subject of much violence at the beginning of the film perpetrated by those in authority (the school truancy officer) who is supposed to show a good example. His mother is a scatterbrain and a pushover who shows little interest in her son and doesn’t discipline him for his antisocial behavior. All the examples in Alex’s life are either perpetrators or victims of violence. The city itself is full of eccentrics in strange garb and Alex sees it as a playground for his sexual appetite. Is Alex a chooser of his destiny or was it chosen for him by a world full of violent men and sexually submissive women?
When Alex is incarcerated he agrees to undergo aversion therapy to become a free man, but when he realizes the unpleasant nature of the therapy (having his eyes forced open and his head held rigidly forward while being injected with a drug that causes extreme nausea) and takes back his consent, the violence is continued against him.
Kubrick further blurs the line between justified violence and revenge when he makes two former gang members police officers. When they commit violence against Alex for past infractions they become thugs in a uniform rather than representatives of the law.
There are many other examples of how violent the world is in Kubrick’s London, but the main issue he treats in this film can be summed up in this question: Does a released convict have the right to defend himself from becoming a victim of violence when he has in the past created victims of violence himself? Kubrick gives you the scenario with this film; you decide what the answer is.