You know how some authors, especially fantasy authors doing the whole spiritual-magic gig, will bring forward the "all gods are really one god, because uber-god is Goodness/Light/Love/Insert-virtue-here" trope? (Eg. Katherine Kurtz and Mercedes Lackey.) You know what that really reminds me of? That deeply horrifying short story Barbara Hambly wrote for Gaiman's Sandman anthology, "Each Damp Thing". There's just something intensely cannibalistic about the sentiment, especially in the mouth of a member of a culturally imperialist group. It's like syncretism turned inside out--not preserving individual practices, but taking away their weight until they can be waved off as surface trappings.

I've seen the principle argued persuasively in actual theology, notably some branches of Judaism. But the Western literary expression of it generally seems to be all about appropriation and how reincarnation can magically erase ethnic, cultural, and religious boundaries, totally ignoring the implications of actual lived experience and memory in each life.