I'm with you on this one. Much as i like to read the stories, surely folklore and mythology are just the 'cod' science of their day. An explanation of how something 'ancient' came to be where it is. I heard a programme on radio 4 a few month's back that was about 'oral tradition' the guy interviewed on the programme stated that he'd done studies all over the UK and the conclusion drawn was that after 3 or 4 generations, word of mouth facts cannot be proved or disproved as apsolute truth, it gets a little like 'Chinese whispers'. I think he said a period of 120 years or so was the apsolute maximum that folktales that had become 'fact' could be varified or not.
I mean we all take Harvest festival to be an 'ancient' custom, though another of those elusive Radio 4 programmes said that it was 'invented/ reinvented' by a vicar in the mid nineteenth century.
An Re: the Christianisation/demonisation of older festivities, well isn't the whole 'Christain Year' just a blanket overlay, give or take a few occations of earlier celebrations. I read in Ronald Huttons' book, The Ritual Year that Christmas was originally in springtime (which would make more sense) and was only moved due to those good christain folk still observing those alledgedly 'heathen' mid winter piss ups. Er, I've strayed off the point a little...sorry about that! I'll shut up now : )