I’m not sure why it’s a big deal just because Mr Musk had a few drags and a glass or two of Scotch?
Because he’s the public face of a very well known company who has started behaving really erratically due, apparently, to lack of sleep and drug use. If people want to have a drink or smoke dope in private, that’s fine, but his behavior raises doubts about his suitability to run his company. He’s a public figure by his own choice, so his behavior is rightly held to a different standard than average people doing stuff in the privacy of their own home.
One legal point is that alcohol clears your system within hours, so having some drinks before bed isn’t a problem for taking a sobriety test the next day. THC takes much longer to clear your system, as I understand it, so you can fail a drug test days after smoking. If Tesla ever fires someone for failing a drug test, then that person’s lawyer’s first question will probably be why Elon Musk wasn’t fired despite publicly smoking dope. If I was a Tesla shareholder, I would be very concerned about his behavior.