They didn't have a scientific proof that smoking was bad for you. Just like we don't have the proof that social media is awful for you and that Trump is a cult.
Cigarettes were recognised as the cause of lung cancer in the 1940s and 1950s, with the confluence of studies from epidemiology, animal experiments, cellular pathology and chemical analytics
And to think that in the 1920s, doctors prescribed cigarettes for weight loss. And now the tobacco industry is moving on to weed, and repeating the same marketing tricks that they used to sell cigarettes nearly a 100 years back ...
It seems the case. I used to think weed was for enlightened individuals given how it was portrayed as a natural alternative to pharmaceuticals (e.g., for pain or psychological reasons). Many forms of media would discuss it positively. But it is still smoking and how many people really have medical justification for the usage?
Mushrooms have a similar portrayal I would say as some god-given superfood.
Looking at smoking rates for people in the US - it peaks for men in the 1950's. I'm not saying studies and taxes and PSA's did nothing but on some level I think most people had a pretty good idea that smoking was no good long before they ever saw scientific proof.
I think those studies, taxes and everything else was as much an expression of that thinking as it was an influence on it.
https://tobaccocontrol.bmj.com/content/21/2/87