Greg, perhaps ancient Britons and other peoples throughout the world had the same beliefs as Africans about the power of a person's true name, and that to avoid speaking and sharing that name, throughout the world, people had the custom of using one or more nicknames to refer to an individual.

But, on a less serious note, I had a uncle whose name was "Wilbur", and when we were young my sisters and I started calling him "Uncle Willie Dillie". That name was a lighthearted term of affection. We certainly didn't snicker when we said it as we didn't associate the name "Willie {Willy} with a man's sexual organ. And we didn't know any Appalachian ballads so we didn't associate the name "Willy" with any murderers.

I'm wondering-do people here agree with Ptarmigan's observation that Willy has been a common name for murderers in Appalachian ballads and other American songs?