But that's the thing: The Dark Side predates even the Sith, both the species and the Order. No matter what, there's gonna be some people who embrace the dark side, and then some people who embrace the light side. The Je'daii are, as far as we know, the earliest unified practitioners of the Force, and they follow a path somewhere along the middle, with maybe a slight slant towards the Light Side. They predate the Infinite Empire by about a millennium, so for that time there was no light or dark order. By the time of Dawn of the Jedi, the Je'daii have fallen closer to the light, while the Rakata have clearly embraced the dark. The Force Wars will seal the deal for the next 25,000 years, forever dividing Force users between the light and the dark. So no matter what, there always is a yin and yang to the Force. It doesn't matter what you call the practitioners of each, since the Force is eternal, Jedi and Sith are not.