In the 50s, black people sat at "whites only" lunch counters. They were breaking the law. Were they irresponsible?
It wasn't illegal, it was forbidden by those establishments and sitting at a lunch counter doesn't cause accidents. Buses, cars, trucks and planes don't crash, people don't fall from girders or off of ladders, they don't run their hand through a table saw. That is an act that hated someone for their skin color and perceived inadequacies. That's not a good example and it wasn't nationally illegal. It was ignorant people forcing their will on others and taking away the rights from those whom they hated.
Look at Prohibition- the Mob made millions, people were killed and lives ruined by booze. Some others made fortunes (Joe Kennedy, among others) and Al Capone fed people by funding soup kitchens during the Depression in an effort to help people who were poor, like he had been. Also, he is the one responsible for the date being on milk cartons because he had been given spoiled milk as a child and he hated it enough to do something about it when he had the opportunity. He did some good things, but that doesn't make him a good person, overall.
Bottom line- working for an employee comes with some agreements. If the company requires employees to not use drugs and the employee agrees to this going in, they have no right to use it. If they agree to a contract with this agreement and intentionally use the drug(s) that are to be avoided, they have defrauded the company and breached the contract. Hopefully, they didn't harm someone in the process. Look at employee theft- it's rampant and everyone I have talked with who did this justified it in their mind in some way. They all "deserved it", it was owed them for some reason, or they "wanted to get back at their employer/company". I can't think of many who weren't drinkers or drug users. A past CEO of Harnischfeger Industries lied when he was interviewed and bilked the company out of millions. Turns out, he was in the throes of a huge mid-life crisis and got caught up in drugs, drinking, spending money he didn't have in order to impress women, etc. Was that his "right"? Did he "deserve" that job?
I think not.