There is actually some degree of argument for this. If you've done the library story arcs and seen the history of how the white mage became the black mage there's this bit about how he says that 'an ultimate white magic doesn't exist but an ultimate black magic does exist' and as such then decides to pursue that "ultimate" form. In a sense it could be argued that an "ultimate white magic" can only exist if an "ultimate black magic" exists first, to give it a reason. So in a round about way he could actually be still pursuing an "ultimate white magic" by becoming a form that will essentially require its creation and being. This is supported also by discussion of the state of affairs in Mapleworld being somewhat bleak, there weren't any real "heroes" around at all, but the existence of the black mage brought about those "heroes".
So I don't really know if you could call him a "good guy", but it might be that he's not necessarily entirely evil... just looking at a "bigger picture" of reality so to speak.