Yes Vampyre, I absolutely would drink a glass of wine with my adult child, but I wouldn't get fall-down drunk in front of them.
To me, getting drunk and taking drugs are something people do with peers. That may well be the culture and social habits surrounding the way I am used to taking them, as much as any moral judgement however.
If we lived in a society where drugs were more in the open, who knows?
I also think I feel uncomfortable with coke specifically because of the very addictive nature of it. I personally wouldn't feel comfortable doing it in the same way I wouldn't feel comfortable smoking a cigarette with my child, I really wouldn't want to encourage them to do something so potentially destructive.
I suppose however it's also partly to do with the social situation. I could imagine, at a stretch, taking a line of coke if i was with my adult child, if we were doing something totally out of the ordinary like trekking up a mountain in South America for example, perhaps. I don't know. (In RL, I have chewed cocoa leaves while trekking up a mountain in South America in RL. They didn't make me high, they just took away my fatigue and appetite, which is what they've been traditionally taken for for centuries).
But certainly not coke in a social situation.
For other drugs, it would depend on the drug. Ones which make you totally out of it, no. Ones which have a mild effect, and are not addictive, then possibly.
FWIW I do know people in their 30s whose own parents are creative types (ex hippies) and on odd occasions (like festivals) take drugs with them / in front of them. It doesn't seem too weird once you're used to it, more just a little eccentric. I've not got a problem with it. (We're talking psychedelics and hash/weed mainly, not coke).