? In case anyone else is looking for it.... "The waltz is magnificently improper -- the art of tone turned lubricious. There is something about a waltz that is irresistible. ..."
H.L. Mencken, 1919.
https://books.google.co.uk/books?id=rqThBwAAQBAJ&pg=PA316&lpg=PA316&dq=H.+L.+Mencken+quotes+waltz&source=bl&ots=GrciilAp5O
Unfortunately I couldn't actually find the quote about "banning pornography" :-( That would make a much better t-shirt.