This is what I meant by assuming you know what Lucas means by balancing the force. While it makes sense to a normal person, or maybe just gamers/D&D players, but it doesn't seem to be what's implied in the movies.
I'll go back to my spinning plate analogy from a while back. So imagine you're happily spinning a plate on your finger, it's perfectly balancing and spinning real good and then some bully wanders by and decides to throw some mashed potatoes onto your plate and all of a sudden it's thrown out of balance and falls off your finger.
The plate represents the force and the mashed potatoes represent the sith (or other darksiders), the sith are like a stain on the force and their presence gums up the works, eliminate them and everything is ok.