Some people need weed.

[Razzle]

And how accessible and well-known was it? It was probably almost as obscure as salvia divinorum is today. 

Just like today, that depended on who and where you were. Marijuana use rates amongst blacks and latinos were high enough to garner Federal concerns, and indeed, one reason it was outlawed was because such outlawing was seen both as a demotivator to  Mexican immigration and one more petty injury to be inflicted upon blacks in the days of Jim Crow.

This is a pretty interesting article about the topic, covering particularly the influence of Mexican-American labor relations:  https://libcom.org/library/4-mexican-ame...-1930-1937

Thanks for the info. It points to another important difference between then and now that I hadn't considered: the association with blacks and South American immigrants was stronger (these days the rate of use is no different between blacks and whites), and the stigma against things associated with blacks and South Americans was stronger among white people. Nowadays, especially among young people, there is no race-related stigma at all. At least not in the US or UK.

In fact I would put money on it being the middle aged and older who would by far complain the most if cannabis were legalised and alcohol banned, in part because most alcoholics are middle aged or older. Young people would be shocked at first and worry about what they'll do when they go out, but once they'd gone to a bar, pub or club and found that many of the strains on sale boost energy and confidence just as alcohol does, without making them crappier dancers or making them throw up, they'd accept it pretty quickly.