So, for the past few years I've had a passing interest in the very elusive Cathars, and by extension their Balkan cousins- Bogomils. I've read into the "sceptical camp" and the "traditional camp" of these things, and I do recognise that there is no real generalised and clear scholarly consensus on the subject, but I'm admittedly a little confused and haven't found a satisfactory answer. A lot of the debates I've seen are on the semantics of the term "Cathar" and whether any group actually self-identified as them, and I've also seen the debate on a unified Cathar antichurch, but my main question is was there any form of dualism in Western Europe at all at the time according to the sceptical camp? Sure, they may not have been unified and they may not have had any organised structure, but is there a grain or truth in any of this? Was there any vague set of dualistic heresies in western Europe, potentially originating from the Bogomils or even arisen independantly?
At the very least the Cathar existence in Italy is well attested from documentary evidence; this sect is certainly dualist and includes both moderate and extreme positions (skeptics do not "contest the presence in Italy in the second half of the thirteenth century of a hierarchically organized and theologically dualist movement" Cathars in Question). The skeptical position generally believes that there is no evidence of any other dualist heretic groups in western europe. RI Moore, a prominent skeptic, lays out his position in his book The War On Heresy that explains all references to Western dualism/Cathar heresies (Rhineland, Languedoc, Flanders etc) as being motivated by a belief that dissident groups tend to be recognized as heretical by the church and classified according to a pre-existing rubric that goes back to Augustine's study of heresy.
Cathars in Question is still the best source on the debate. The book came out of an academic conference on the existence of a Cathar church. Chapter 7 is an excellent discussion on Eastern Dualism and what influences it might have created in the west but the entire book discusses what evidence there is for other dualist heresies in addition to Cathars (indeed it is hard to grant the existence of one without the other following). Cathars in Question The War On Heresy