As far as I can tell, "Source" seems to be a play on the old-style definition of "sorcery" as a mix of necromancy, demonology, and other assorted "black magic". I have no idea how canonical this is, but my impression from the alpha is that some of it could theoretically be used for good (or at least non-bad) ends, but even that path is the sort that's "paved with good intentions".
