I would just like to caution you, Pravchaw, that there is a significant distinction between drinking/drug abuse and the disease of addiction.
Addictive disease is not cured by nurture. It is a permanent, lifelong, irrevocable change in the structure and chemistry of the brain. When we mistakenly believe that we can influence this biological illness by our love and nurture, we will be shocked when the addict not only does not get sober, but resists and resents our efforts to change him.
So do continue learning about addiction, for if your son has addictive disease, what looks like loving concern and support from the family could be part of what keeps his addiction enabled. We do not cause addiction but we most definitely can contribute to its progression by rescuing the addict from the consequences of using.
Your son is addicted to pot, in your opinion. This means he will use any means to pave the way toward an easy life as an addict. Pot is also demotivating. So a nice room in the basement and loose change is the last thing a pot addict needs. Be very careful. Keep learning. When the family starts recovering in the right way, it can hasten a bottom for the addict. Not always. But it increases the chances.