JDM's essay is as good and simple an explanation as I've found:
What is the Dark Side, exactly? Well, technically speaking, it's an underlying energy that guides people-for better or worse-in the Star Wars universe. But in the big picture, the Dark Side is a form of Obsessive Compulsive Disorder. Not a clinically diagnosed form, mind you. (And before I get emails from OCD readers: Please, I'm just trying to make a point here.) But rather, it represents "order." It represents the undying allegiance some leaders have to their vision of how things "should be." Politicians consolidate power for plenty of reasons-like money and job security-but it's the belief that they're somehow performing a vital service that clears their conscience to do this. It's not that they haven't got values; it's just that their values are totally messed up. They truly believe in their vision for society. This is what justifies everything they do.
This jives with my argument - the Dark Side is not a different type of force, but an imbalance in the force's whole nature. The Dark Side is a component of the complete force the Jedi's employ - the difference is that they can see things in broader terms than simply "what I want and how to achieve it." Overemphasis on the power to change that which one cannot accept is a road to suffering, since absolute control is never achievable - it is simply not an option, even for one so seemingly powerful as the Emperor. Darth Sidious is correct: "All those who have power fear to lose it" - and their fear is well founded because often that power represents an imbalance in the natural order. Perhaps even the power of the Jedis was too great and needed balance (hence, Anakin).
There are things you can control and things you can't; there are some events you should accept and some you shouldn't. Knowing which is exactly what true wisdom is. Fixating on how to change what you cannot accept is the Dark Side - intent plays a very small part.
This is precisely why we should hold those whom we charge with power accountable: not for their good intentions, but for the outcomes of their actions and policies. Principles are important, clear positions are vital - but even more important is knowing the limits of principles and positions. They can guide us, but they cannot fully model the complexities of life. The utilization of power is not the path to realizing every good that can be achieved in life. It takes wisdom, compassion, and humility to determine when to employ one's authority to alter outcomes and when to accept that a seemingly unfortunate situation is, in the final analysis, a sorrow one cannot avoid.
UPDATE: To pointlessly continue the speculation on Galactic Republic histrionics, Reason magazine's blog has a good defense of the Seperatists with a revealing look at Lucas's politics about "free trade".Read this article