The balance the Jedi seek is an almost buddhistic one, you try to live in harmony with your surroundings not giving in to egoistic desires. The dark side of the force is not considered a true part of the force, it's more like a cancer that corrupts the natural order of things.
I mean how can a Jedi code speak about balance, when the Jedi order is all about good-goers and destruction of evil.
True balance is quite hard. Getting in harmony with the two opposite Forces.
Neither Jedi nor Sith actually seeking any balance at all. If anything, the right opposite.