i think in general it is due to cognitive dissonance, which kicks in when ideas are tied to strong emotions. In the case of propaganda those emotions are induced by the language used to describe those concepts. This is definitely on purpose.

But i have seen this effect with way more meaningless things as well. For example, i am a huge coffee nerd and when i tell people about specialty coffee, what it is and how i can taste, even while making an effort to not belittle anyones personal preferences, people still get weirdly defensive about their tastes.

So i really think it is a more general societal problem of valueing knowledge over the process of learning and understanding. This in itself is a useful trait because it makes people way more susceptible to propaganda