Harriet; I have nothing much in the way of religion, or even morality, but I do recognize a code of behavior of sorts. I do know the worst sin — perhaps the only sin — passion can commit, is to be joyless. It must lie down with laughter or make its bed in hell — there is no middle way.

Dorothy Sayers (1893-1957) English author, translator

Gaudy Night, ch. 23 [Wimsey] (1935)
    (Source)

Sometimes paraphrased, "The only sin passion can commit is to be joyless."