> did people not believe crazy things in the mid-20th century?
Why is that even a question? Of course the crazy was around. It was just much more difficult to spread it around. You had 'zines that were available. You had AM and shortwave radio programs. Just by telling someone you listened to AM/shortwave content already set people in the correct frame of mind of where the information was obtained. In modern times, it's everywhere on the socials. It just so happens the time the socials were gaining usage with people that specifically do not know critical thinking nor have been taught the ways to investigate sources.
The internet as been an equalizer for everyone doing anything. As much as it has done for retail, it has also been huge for not just the conspiracy theory sites but propaganda from anyone including foreign actors.