We are discussing cannabis use, and you throw out the term addictions and these people becoming unemployable? Cannabis is not chemically addictive like, alcohol, tobacco, caffeine, sugar (some will disagree on sugar), opiates, cocaine, hundreds of prescription drugs. Do you want to prohibit all these addictive drugs? Do you want to make users of these drugs criminals and ruin their futures for personally consuming these substances?
There are millions of Americans who use cannabis and work and run businesses just like the alcohol users and the caffeine users.... and the....
Um, marijuana is most certainly addictive. And the reason these people become unemployable is that they damage their brains--they develop psychiatric disorders that make them unemployable. But even in the absence of overt psychiatric disorders, marijuana use affects the ability to find and keep a job.
This study looked at unemployable youth, and found that (not surprisingly) marijuana use was significantly associated with unemployability: Not in education, employment, or training status among young swiss men. Longitudinal associations with mental health and substance use.
A problem with marijuana is that it inhibits both ambition and initiative. Being unmotivated to do anything really does make people unemployable.