It sounds to me like some of your friends have been using a substance to fill a void in their lives or avoid facing some issues, this is really terrible and I understand.
Truth is, there are just so many ways people can use and abuse things and it's wrong to blame anything in particular. If people sniff glue to mask a problem, you wouldn't say glue has a dark side. Yes glue is can be toxic and extremely harmful, but it doesn't have any intentions or predispositions.
Don't get me wrong, I've had similar views in the past, it's just where I'm at now from my own life experience.
I agree that, being stoned every minute of the day is not a good idea, maybe you're trying to say cannabis is more toxic than people think?
Who said productivity and ambition are absolute values? Are there some tablets of stone somewhere?
They usually never drink alcohol I find - or very little.
I know about 5 people who fell into this trap and when (some) of them packed it in have enormous regret. My point is that this isn't talked about with cannabis.