Yet another Harry Potter skeptic converted! (I, too, was once one.) Echidne has been reading the books and has, as usual, interesting thoughts on the matter. One very crucial point she brings up is that the whole wizard economy seems very ill-formed; everyone's still on the gold standard (and a gold reserve whose price is apparently unaffected by supply and demand here on planet Earth). The economy also seems to rely very, very heavily on slave labor—something that only Hermione (and at one fleeting point in the sixth book, Harry) seems bothered by. It's all very unstable. In fact, as with the thesis that the Civil War wasn't really about slavery, I'm sure you could find some sort of economic rationale for Voldemort's de facto secession from the wizard world.