It's bad when the Celts are used as a tabula rasa to provide a convenient, and completely imaginary, "ancient lineage" for a lot of half-assed, new age twaddle. How to be a druid in ten easy lessons. That sort of thing.
I'm not talking about the etherial twits who run around in white dresses spouting pompous poetry, either. I mean the brainless fools who really think they're druids and build castles in the air ( Inside their crania.) about the wisdom they've "inherited". The simple truth is that we know very little about ancient Celtic religion, and the little we really do know, from archaeological evidence, shows something very unpleasant.
I've known quite a few morons who yap about the ancient wisdom of the Celts. Usually, they're the sort who really shouldn't be without a keeper.