Sorry if this is off-topic, but I think an extremely important thing that Karl Popper described is https://en.wikipedia.org/wiki/Paradox_of_tolerance

I believe that in most of the EU countries, and in the US, not understanding the "paradox of tolerance" is the number #1 threat to those societies.

What the "paradox of tolerance" explains, is the logical fallacy which the enemies of society hide behind, to prevent being punished and destroyed. Unfortunately, in most cases, they do it successfully, and each and every step leads closer to the destruction of those societies. It basically goes like this: "if you're tolerant, then you must tolerate my intolerance". In other words: "if you try to destroy fascism, you're a fascist, because only fascists try to destroy other cultures/ideologies".

In reality, killing a murderer is not murder - it's self-defense, capital punishment, etc. Taking stuff by force from a thief/robber is not theft/robbery - it's restitution, confiscation, compensation, etc. In the same way, destroying a fascistic culture/ideology is not fascism - it's whatever you want to call it, etc.