I just found out that there exists an earlier term for semantic stopsigns: a thought-terminating cliché.

A thought-terminating cliché is a commonly used phrase, sometimes passing as folk wisdom, used to quell cognitive dissonance. Though the phrase in and of itself may be valid in certain contexts, its application as a means of dismissing dissent or justifying fallacious logic is what makes it thought-terminating.

The term was popularized by Robert Jay Lifton in his 1956 book Thought Reform and the Psychology of Totalism. Lifton said, “The language of the totalist environment is characterized by the thought-terminating cliché. The most far-reaching and complex of human problems are compressed into brief, highly reductive, definitive-sounding phrases, easily memorized and easily expressed. These become the start and finish of any ideological analysis.”