Believe me, I would be happy if no one used drugs too. I agree with you that it is hard to change your circumstances if you are not clean and sober.
And true too that drugs can bring somebody formerly well-off to to poverty through a bad addiction. We've all heard the stories of the banker/stockbroker/ trust fund inheritor blowing all their cash to finance a cocaine addiction.
But I don't truly believe that pot can impair somebody's work ethic enough to bring them into systemic poverty. Other drugs yes, pot no. It's a bit of a kiddy drug. You could fail out of school on it, maybe lose a job on it, but not be totally unable to care for yourself and fall into poverty.