Certainly not justifying the use of any drug, but if you check the literature one of the easiest ways to get off of Heroin addiction is by using LSD. It tends to lessen or eliminate much of the physical problem associated with "cold turkey". I'm not sure if this is how they used it, but there are clinics in Mexico that are based on this.
The justification for people going in to Synanon and being there forever is based on a type that's generally called "addictive personality". They definitely exist and are found abusing almost anything they can get their hands on. With alcohol there are genetic markers for some groups of people who are particularly affected and easily "hooked". These people are not the same as social drinkers, smokers or drug users who can become addicted but with some effort can quit permanently. Physically dependent and psychological addicts are notorious for failing to "clean up" on a long term basis.