The film's iconic image is Alex strapped to a chair, eyelids held open, being forced to watch snuff films. Yeesh.
The scene is made to be as barbaric as possible to convince the audience that this technique is a Very Bad Thing. The audience totally identifies with Alex as this point (or at least feels for the dude). He grimaces and screams. His face is shown twisted in agony in extreme close-up—notably unlike Alex's victims: the people Alex kills and rapes are usually filmed at a greater distance.
Putting aside the dehumanization of Alex's victims—we basically see the victims like Alex does, as anonymous bags of meat—Kubrick makes the Ludovico technique super-duper brutal to get viewers to question whether or not it is right to subject anyone, even a violent criminal like Alex, to this kind of barbaric procedure.