It's easy to buy into propaganda when you have no first-hand experience with something. Access to information was much more limited back then and censorship was much easier. It's not like most libraries would have a cannabis section in the 60s.

If I were constantly told by a number of authority figures that Argentina was a war-torn shithole with rampant poverty and violence, I'd likely believe it. I've never been there, I don't know anyone from there, and I have no reason to suspect those who I trust are liars.