"Most forbidden of all" means that: Holocaust denial. People that were murdered there were murdered accidentally.

https://old.reddit.com/r/EnoughMuskSpam/comments/1f8jyxn/increasingly_close_to_questioning_the_official/

  • GrouchyGrouse [he/him]
    ·
    15 days ago

    Because asking a question in good faith is one of the most honest things a person can do. It's right up there with admitting you don't know something. When used correctly these are humble things, earnest things, tools that can help you grow.

    So it is naturally grating and it inspires revulsion to see a person misuse those rhetorical tools.