Lets go through this logically, one I will assume you understand how the mind stores memories. I will also assume you understand how chemicals reward you in the brain. Basically I'm assuming you did your research on how the brain basically works. I assume you know what an actual disease is and how it effects the body. There are biological diseases and chemical imbalances no such thing as a psychological disease. Now a person does not get addicted to anything, they, overtime, learn to do something based on the reward (stimulus) the brain gives them. Touch the stove multiple times and get burned you learn not to touch it. You drink or do a drug and it makes you feel good and you want to keep doing it. You do it until it becomes habitual, your still not addicted you've just formed a habit or learned behavior.
Now when the drugs or alcohol wear off you go through a withdraw, your body is jacked up from depleting certain vitamins and electrolytes from your system and you created chemical imbalances in your body. Oh snap your going through a withdraw, no, you have removed a toxin from your system and its now out of whack and it sucks and makes you sick. You don't like that feeling so your brain panics and demands to be normalized. So you have a choice, go through the withdraw, get your levels back up and get healthy or use again. Most people will either not like the feeling and quit never to use again or they will use again to not feel the symptoms. Either way they don't need the drugs or alcohol, if you stick them in an environment where they don't have access to their "doc" they will get clean. Their body will rebound and the mind will begin to clear up and rebound as well. Then you need to, with the help of a professional, work through the issues that caused you to use in the first place.
Do I believe some people are to emotionally weak to do this alone, YES. That is why I still believe a rehab is needed. People need a safe place to escape their current environment and get clean and healthy. They then need to get the psychological help they need to find out why they were choosing to use and not use again. This is done with the responsibility placed on the shoulders of the person responsible. They are not victims, people don't go out and say I' m going to snort me a gram of AIDS. They do say I am going to drive to the LQ or meet the pusher man. Most people with disease wish they didn't have to take meds to get well. They don't rush to the pharmacy shitting themselves in anticipation of that next score. No people choose to get high for reasons that need to be explored and worked through. They are responsible for how they got there and they are responsible for stopping. So stop the lying to them and telling them they have a disease and are addicted when they choose to use.