>Doing hard drugs, as is alcohol, is not part of any legal contract.
Right but there's more to life then legal contracts. Many companies want a very close knit team. Part of this closeness comes from participating in extracurricular activities.
Look beyond the legalities. If a team expects this and you know you don't want to provide this to the team, THEN why are you choosing to work for them? Why are you insisting on using the law to protect your employment for a company that obviously doesn't want you?
Join the team that works for you. If you withdraw from all hard drugs, JOIN the company that doesn't HAVE that culture or leaves that CULTURE as OPTIONAL.
For this guy in the article he joined a team that wasn't a good fit for him. Him getting fired was correct, he never fitted in. But I will say what's likely unfair is that the "fun" part should've been part of the job description. They should've put it in there, not explicitly but implied it such that this guy knew what he was getting into.