ok lets look at this from another angle. can any1 name a lightside sith, that remained part of the empire and didn't turn into a jedi,
i'm thinking opening an puppy orphanage would be a good example (ok maybe that is extreme) but seriously is there examples of light side sith?
Revan. It was always his plan to do the 'right' thing to save the Republic. Becoming Sith was merely necessity.