Please don't take my word for this. Most of the problem with this sort of thing is people taking what they are told for facts because somebody sounds credible.

Looking up info on May poles. The poles are indeed ancient, but ribbons are 19th century. And there's no evidence for phallic symbolism - mostly just celebrating "yahoo! It's SPRING!". My source is Ronald Hutton in The Stations of the Sun, Oxford Univ. Press, 1996. Now, that's pretty old, and it seems to me that academic research falls into disrepute every decade or two. Everyone has an axe to grind, it seems. I don't know what current scholarship says about it.

I have read (maybe Sutton, again, can't remember), that the elaborate ribbon interweaving was invented for the London stage, and people thought "hey, that's cool, let's do it like that back in the village." And so was born an ancient pagan fertility ritual. I can't cite a source on that one.

James Frazer's The Golden Bough carries the blame for a lot of this. Written before any kind of scientific standards, it spun a theory so compelling it is still believed. Which is that everything harkens back to pagan, tribal practices of pre-history, especially the king-sacrifice - done to insure fertility and the return of summer. (see the original Wicker Man and Stravinsky's The Rite of Spring). Frazier is sort of the the pagan movement's Ayn Rand, I think.

If John Biggun's WWI historical fiction is to be believed, this stuff was like catnip to nationalists trapped in the huge empires of the early 20th c., encouraging claims to pre-empire, pre-Christian tribal identities. This encouraged interest in folk customs (but now they were "folk rituals") and unfortunately, also in racial/cultural purity.

Somewhere in there was the academic belief that once upon a time humans had perfect understanding of why they did things, but in passing it down, it got muddled. So, by tracing things back, finding the original, or as near to it as they could get, they could figure out what that was all about - religion being the main field of study. We still have folk song collectors and singers doing that today. Though in most cases we aren't taking it back to the ancient Greeks. (see The Myth and Ritual School, J. G Frazer and the Cambridge Ritualists, R Ackerman, Routledge, 1991)

I'm no scholar, I just happen to have read up on these things, and it's very possible I have muddled ideas, or have picked up ideas that have been discredited.

I think I'm on pretty solid ground when I say the May Day dawn dancing started in 1920's Oxford when the local morris teams decided to entertain the crowds gathered to hear choristers sing from the college towers at dawn.