Folk etymologies are fun!....and in the words of Cecil Adams, “some day one of these cute stories will actually turn out to be true!”
That’s what I’ve always heard. If a phrase origin has a “tidy” or “cute” explanation, it’s probably made up. Like “Mafia” coming from the words ma and fia meaning “my daughter!” in Italian. Not true. Nor is it true about “For Unlawful Carnal Knowledge”. Although I’m not sure about “In like Flynn”. Supposedly referring to Errol Flynn’s sexual escapades. Maybe.