Depends on the drug of course, but since the vast majority of these substances are both highly addictive and also severely impact your ability to operate heavy

Depends on the drug of course, but since the vast majority of these substances are both highly addictive and also severely impact your ability to operate heavy machinery, people who test positive for (certain types of) drugs are obviously more of a liability on a factory floor. I don't think it's stupidity that makes employers hesitant in this case.