Many a true word is spoken in jest -- first attributed to Chaucer and updated by Shakespeare: https://www.phrases.org.uk/meanings/many-a-true-word.html Fact is, the Overton window is wider for humor than for serious discourse. Twain could say what he did as a joke, believing that many people would read 'between the lines' without directly offending the powers that be. That was what nursery rhymes were about: everyone knew which politician was Humpty-Dumpty. You didn't have to say it directly, and if you did it might have cost you your head.