The The Night Battles by Carlo Ginzburg is a fascinating book, a microhistory of the folk custom of the Benandanti in 16th and 17th century Friuli, whose members were persecuted as witches by the Inquisition. In the book, Ginzburg makes two very interesting arguments. The first is that the Benandanti represented the remnants of a pre-Christian, pagan fertility cult that had survived until the early modern period and had incorporated Christianity into their practices. Based on a couple additional case studies, Ginzburg also argues that the Benandanti were just one part of a continent-wide tradition that covered central Europe and as far east as Livonia. How widely accepted are Ginzburg's arguments? Was there a pan-European agrarian cult descended from pre-Christian fertility rituals?
I don't know of a single historian of early modern religion who disputes that there were pagan holdovers in European folk beliefs of the sort that Ginzburg describes. Another book that deals with these sorts of beliefs is W. Behringer The Shaman of Obersdorf (English ed. Virginia 2004).
In Behringer's case, it's abundantly clear (and I think this is also the case for Ginzburg's subjects as well, particularly Menocchio in The Cheese and the Worms) that his subjects view their folk beliefs, which we (and the inquisitors) identify as Pagan holdovers as entirely consistent with their Christian worldview. These people did not think of their "Pagan" beliefs as inconsistent from their "Christian" ones. They were all part of the same supernatural worldview.
There are lots of examples of holdovers from Pagan fertility rituals, and how they got tangled up with the rudimentary Christian education that rural people had. My personal favorite is from my own research: in the Spring of 1575, a Catholic priest from the Archbishopric of Cologne traveled to the remote village of Upper Tudorf. He was horrified to see the local priest (who was also a barely literate peasant--he couldn't even speak standard German, only the local dialect) processing through the fields with holy water, singing Lutheran hymns. Somehow these people had managed to tangle up Lutheranism, Catholicism, and their agrarian folk beliefs.
There is no evidence for the idea, which was first put forth in 19th-century England, of an internally-consistent secret cult of crypto-Pagans that persisted from pre-Christian days. For more on the development of this idea, see R. Hutton The Triumph of the Moon (OUP 2001), which is about the development of English Neopaganism in the 19th century.
So the question I guess I have to ask is, does Ginzburg claim these cults were all related/cooperated? Or does he claim that there were merely pagan remnants throughout Europe? I've never heard of any pan-European pagan remnants before. However, aspects of paganism survived in many parts of Europe, ranging from traditions to outright acceptance of pagan rites and practices under an otherwise Christian veneer. Modern Mexico (and colonial Mexico too) is a good example of this, but hardly unique. In Wales for example, at least up until the 1930s there are stories of witch doctors on the outskirts of every village, theoretically descended from pagan traditions but otherwise tolerated by the Church. Indeed, this sort of 'wild-woman' was not uncommon in Europe during the Medieval and Early-Modern period, and I suspect that the Benandanti had more in common with that facet of paganism than anything else.