The sith and jedi are just organizations that people follow by the code lifestyle ect expect we know half the time a sith is a sociopath.
But look at revan he fell to the dark side didn't want to join the sith because he was patriotic about the republic so assumed the Dark Lord split the republic between sith and republic to seize it and prepare it for the Empire. He became a Necessary evil for the greater good so yea a dark side jedi does make sense