It is, in germany, atleast.

Same reason why people who try an deny the crimes of communism are allowed to exist. People can say what they want as granted by the first amendment. Its up to the ones who know differently to call out the bullshit. However, there are some forms of speech that are not allowed, such as: Obscenity, Fighting words, Defamation (including libel and slander), Child pornography, Perjury, Blackmail, Incitement to imminent lawless action, True threats, and Solicitations to commit crimes. Some experts would also add treason, if committed verbally. https://www.freedomforuminstitute.org/about/faq/which-types-of-speech-are-not-protected-by-the-first-amendment/