This really can't be overstated. Propaganda was highly effective even as words on pieces of paper distributed once a week or infrequent AM radio broadcasts.

I believe the old idea that would hold even more so now is that the only defense against propaganda is essentially to be illiterate. It is really hard to propagandize a person who can't read. The more informed a person believes themselves to be about the world from text, the more propagandized they are. I believe that is from Edward Bernays.