Yeah, yeah, I've read the books, I've heard the arguments, I know all about flawed methodology and bogus historiography. Who takes Murray seriously these days, anyway?
An important element is missing here. People believed Murray's theories for years because they're convincing. They have the ring of likeliness to them.
OK, here we are, medieval peasants. Life is hard. We work our butts off sun-up to sun-down nearly every day, and in a good year we raise enough to get us through to the next harvest. Often enough, we don't, and then we starve. Even in good years, the seigneur and the priest have automatic authority over pretty much every aspect of our lives.
We grew up hearing fireside stories, half-remembered, about the Old Ways and the Guy with the Horns. Yeah, I know Father Guillemet says he's bad, but the priest doesn't know everything, anyone can see that. He's a priest, what does he know about real life?
What is more likely than that on the old days you'd go off to the bonfire in the woods, get drunk, dance and screw your neighbor's wife (or husband) in the bushes? Pleasure is rare enough in life, and you have to take it when you can get it. And part of the fun is poking fun at Authority, especially Authority—like the church—about which you really can't help but feel a certain amount of ambivalence. Mix bits and pieces of decayed paganism with the only rituals that you know—those of the church—and voilà: spontaneous folk-diabolism.