I have worked at a place that did not screen out such (a factory, one of the few places, as I understand it, where you could get employed with a record). We're talking about being unable to show up for work or follow simple directions after a week. I can only imagine how they might've behaved in something customer-facing (i.e. flipping burgers).
Now yes, there is the other side of that. There were also a number of folks struggling to fix up their life. These I commend and I helped where I could along that route.
Crap, our anecdotes paint different pictures. Could it be that neither of our samples is representative of "drug users" as a population?
http://onlinelibrary.wiley.com/doi/10.1111/j.1465-7287.1998....
Quote: "Using various measures of current and lifetime drug use and accounting for alcohol-use comorbidity, the authors find predominantly insignificant relationships (both direct and indirect) between drug use and both wages and absenteeism, regardless of gender."
When drugs are legal, holding down a regular job will be compatible with drug use; people will work regular hours to pay for their habit, pick up their drug at the corner market on the way home, and take the equivalent of cigarette breaks.
When heroin was a branded product of the Bayer corporation, one of the founders of Johns Hopkins was a heroin addict; he took pills. (The chief long-term problem associated with regular heroin use is constipation.)
So, no: people stealing to get their fix is an argument for legalization.
(How many people are today "stealing to get their fix" of beer or cigarettes?)