Repeat a lie often enough and people believe it. Especially if you get then angry first so critical thinking is shut down. Help that along with social media echo chambers and 24/7 “news” broadcasts. Add cult of personality around it and you get this.
“The problem with defending the purity of the English language is that English is about as pure as a cribhouse whore. We don’t just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary.” –James D. Nicoll