Doesn't the actual problem lie in the inappropriate attachment of universal value to certain classes? For instance "X is an existential risk" might be a persuasive premise that would convince someone on LW, but would it convince anyone else? If anything, the best argument in the world against X has as its premise "X yields less utility than not X". If people always tabooed words until they reached explicit statements about utility they could avoid more than just one class of wrong arguments. Unless a class is universal (forall X, X yields less utility than not X) classes should not be used. Even existential risk is not a safe class because there are scenarios where humanity living forever yields less overall utility than humanity dying out.