We have to remember that there were a lot more controls over propaganda from other nations just earlier this century than what they are now (e.g. banning communist literature).

I honestly don't see a solution to this unless we have a general increase in the wisdom of the population. Censorship worked when the flow of information could be regulated, but with the internet, it seems unlikely that this is possible (unless you take pains to implement something like the Great Firewall).

Ideas can have a powerful effect on people. The Bolsheviks believed that the world was ripe to adopt communism, forming an international union of communist countries, and this would happen not through war (necessarily) but by people's revolutions in each individual country. When you understand that plan, it makes sense why the US was so paranoid about communism on its own soil.

I'm not saying its communism which will take grip of the imagination of people. But it might be some other radical idea. We need to understand that this is a very real possibility.