These drugs are escapes for people - and a lot of them, especially younger kids get completely hooked on the escaped from reality from these drugs (including alcohol).
We should instead be limit the use of these drugs and have teams dedicated to studying why people are turning to these instead. It's OK to have them on the weekends, but most people I know who smoke weed are on it the majority of the time. Alcohol isn't much better - most do limit it to after hours / weekends, but there are a few who tend to overdo it.
From a biased point of view, I've had a few young family members and friends who turned to weed as their go-to for their daily lives, and it has changed their lifestyle, made them far less willing to live out their life and pursue actual goals. They definitely had both the potential and backing of their families (mid to high class) to do great, but chose to instead live a life of 'rotting away' in their words. Out of them only one has turned their life around (still smoking on weekends) citing that it made them not want to do absolutely anything in their day to day life.