Lucas couldn't figure out the balance of the force thing
Lucas figured out the balance of the Force just fine, but others sometimes screw it up.
During the Yuuzhan Vong war it finally looked like the 'balance of the force' was going to be attained by Jacen Solo since he expanded the normal Jedi powers, brought back old techniques, and even had some force lightning.
Balance was restored to the Force as the result of Palpatine's defeat in ROTJ, and that was before the NJO. What is being described above sounds like yet another kind of notional balance: a "balance" of Force powers, or equivalently a manifestation of Troy Denning's insistence that the light side must be capable of the same Force powers as the dark side. But that is not what the balance of the Force refers to.
The force being neutral and basically a power/weapon and the actions of those using it are what determines if something is 'light/dark'.
According to Lucas there are such things as dark side powers, meaning that they are dark side in nature regardless of how they are used. For example, from Lucas' POV the appearance of lightning identifies a darksider regardless of the context of its use. Lightning would not identify darksiders in this fashion if it were available to either side. This results from the fact that Lucas conceives of the Force as a two-sided energy field with a light side and a dark side. Lightning is considered a dark side power because use of the dark side of the Force is required to conjure it in the first place, not because it's a nasty thing to do to someone.
Hound of UIster said:
There is no "light" side of the Force.
That is incorrect. According to Lucas, his characters, and various EU sources, there is a light side of the Force. It was referred to as the good side in TESB, which called the light and dark sides the "good side" and the "bad side" respectively. The Force is two-sided.
Hound of UIster said:
The Dark Side is by itself an imbalance
As has been made explicit in EU, the balance is
between the light and dark sides, so it makes no sense to say that the dark side is an imbalance. The Force in balance contains both light and dark sides, as was reiterated by the Father in the Mortis arc of TCW. A good example of imbalance would be the revisionist scenario where the Force has no dark side. All of one thing and none of the other can hardly be called balance. In fact, it's as unbalanced as you can get.