Humans are prone to attribute concepts together. By linking together these things they will attempt to try and understand the world better. However these false linkages come often and can be difficult to absolve.

In A Clockwork Orange, there is a psychological experiment called the Ludovico Technique in which the main character is introduced to aversion therapy. Given a syringe that causes pain and nausea, they are exposed to scenes of violence and sex. This transforms them such that every time they see violence/sex, they feel the same symptoms.

It's an inescapable mechanism of being human.