Demolition Man

In 1996, psychopathic career criminal Simon Phoenix kidnaps a number of hostages and takes refuge with his gang in an abandoned building. LAPD Sgt. John Spartan uses a thermal scan of the building and finds no trace of the hostages, and leads an unauthorized assault to capture Phoenix. When he is captured, Phoenix sets off a series of explosives that bring down the building, and when the police search the wreckage, they find the corpses of the hostages. Spartan is charged with manslaughter, and he is incarcerated along with Phoenix in the city's new "California Cryo-Penitentiary", where they will be cryogenically frozen. During their time "in deep freeze", they are to be rehabilitated through subconscious conditioning.
During their incarceration, the "Great Earthquake" leads the cities of Los Angeles, San Diego, and Santa Barbara to merge into a single metropolis under the name San Angeles. The city becomes a utopia run under the pseudo-pacifist guidance and control of the evangelistic Dr. Raymond Cocteau, where human behavior is tightly controlled. In 2032, Phoenix is woken for a parole hearing, but he finds he somehow knows the access codes to the security systems, and is able to escape the prison and begins wreaking havoc on the city. The police, having not dealt with violent crime for many years, are unable to handle Phoenix and opt to wake Spartan and enlist his help. Spartan is assigned to Lieutenant Lenina Huxley to help with acclimation to the future, which he finds depressing. Others on the police force find his behavior brutish and uncivilized, though Huxley, who is fascinated by the lifestyles of the late 20th century, helps Spartan to overcome this, and the two grow close, despite the limitations on displays of public affection.
They attempt to stop Phoenix from stealing 20th century weapons from a museum display, but Phoenix manages to escape. Phoenix encounters Dr. Cocteau during his escape, and though he tries to shoot him, finds himself unable to do so. Dr. Cocteau calmly asks Phoenix to assassinate Edgar Friendly, the leader of the resistance group called the Scraps that fight against Cocteau's rule, and allows Phoenix to bring other criminals out of cryo-sleep to help at his request. Meanwhile, Spartan and Huxley review the cryo-prison records and find that instead of the normal rehabilitation program, Phoenix had been given the information necessary for his escape by Cocteau directly. They also discover information directing Phoenix towards Friendly, and go off to warn him.
At the Scraps' underground base, Friendly is initially distrustful but Spartan is able to convince him of the threat and takes sympathy in their cause given what he has seen above ground. When Phoenix and his gang attack, Spartan and the Scraps ward off the attack, leading to a car chase between Spartan and Phoenix. During the chase, Phoenix taunts Spartan by revealing that he had killed the hostages before Spartan had arrived in 1996. Phoenix escapes while Spartan comes to terms that he had been wrongly charged with the crime. Meanwhile, Friendly and the Scraps work with the police to try to help stop Phoenix and his gang of cryo-cons.
Phoenix returns to Dr. Cocteau with his gang, and as the rehabilitation programming prevents him from killing Cocteau, orders one of his gang to do so. Spartan and Huxley arrive soon after, finding that Phoenix has already left to release more prisoners. Spartan enters the prison alone to fight Phoenix, engages in a violent fight that ravages the facility, and eventually uses the cryogenic chemical to freeze Phoenix before shattering him. Spartan escapes the prison before it explodes and regroups with the police and the Scraps. The police fear the loss of Cocteau will send their society into a downward spiral, but Spartan suggests that they and the Scraps work together to recreate a society that returns some of the personal freedoms that were lost. He then kisses Huxley and the two go off together.

Question: What prevents Phoenix from killing Cocteau?
Answer: The rehabilitation programming