I cherish common usage. I first encountered King Canute (if you insist) in the wilds of collective commonality long before he made his ceremonial entrance into the hallowed halls Educational Correctness. It went something like this:
Pedagogue: "Can anyone tell me who King Canutes was?"
30 eager kids with hands raised: "I can! I can! Me! Me!"
Pedagogue: "Okay then - Suibhne - enlighten us."
S O'P (aged 6): "He was a king who thought he was so powerful that he tried to command the very tides but only got wet feet for his troubles."
Pedagague: "Wrong, you malnourished oik!" (lobs blackboard rubber at hapless pupil knocking him to the floor on which he lies, bloodied, but still conscious) "King Canute was not trying to turn back the tide ~ he was demonstrating that it couldn't be done, in order to deflate his flattering courtiers' fulsome assessments of his powers."
And so the nourishing maternal warmth of common usage was betrayed by the dictates of cold hard fact.   

Similarly Ring-a-Roses was a game we played in all innocence before being told (no doubt by the same teacher) that we were, in point of fact, re-enacting the symptoms of the Black Death. Now, whilst I'm pepared to accept the Canute Disparity as being a genuine instance of folklore simplifying history if only to make a more compact analogue, the Ring-o-Roses IPOF I regard as the worst possible sort of myth-making. Indeed, such mythconceptions take hold like Grey Squirrels, choking the life out of our more delicate native Reds, hence the need for a more rigorous approach to the management of the ecology of our cherished Folklore before it too is pushed to the brink of extinction by facts both real and imagined. This is why I continue to draw King Cnut in the sand, to keep common usage alive, at least until the tide comes in.