I can see how people let the Nazis rise up under their noses.

Poisonous political parties are allowed to grow until they're too big to ban or stop. Huge disastrous wars happen overseas, or on the same continent, or just a couple of countries over. The people or organisations who are supposed to represent and protect us instead endanger us.

If we're lucky, we can go on news diets to protect our mental state. At some point people will ignore the stuff closer to home too.