I think the light/dark sides should have been a Jedi phrase. They saw force users become corrupted by the power of the force and installed a Jedi code which limited how in touch one could become with the force. Because if you grew to powerful with the power it would consume you (unless you take the long and hard path, like Yoda).

On the other hand the Sith simply believe they are using the force to it’s full potential. Some are just in it for conquest, but others (such as Darth Vader) believe they are using the force for the greater good and all the Jedi do is limit their quest for justice. Of course the quick and easy path slowly consumes them. This would have added a lot more depth to the dark side, with multiple beliefs and orders. It also would have benefited the PT (and ST with Kylo Ren) tremendously.

I mean seriously, who in their right minds thinks the “dark side” are the good guys?