The Sith Weren't Always Bad
What should be made clear off the bat is that the Sith didn't just show up like boogeymen one day and start terrorizing the innocent. They were Jedi to begin with - only more radical in their views of the galaxy and what their gifts should be used for. The first Jedi Exiles - the group that would one day found the Sith - were simply one side of a civil dispute within the Jedi Order, known as the Second Great Schism. Whatever extremes each side pushed the other toward, it should be known that at no point did the Sith huddle around a fire and decide to crush all life in the galaxy; they were conquerors in search of mastery over life itself, not genocidal maniacs. They even developed their own Sith Code, opposing that preached by Jedi. Rather than speaking of existence as it should be, they focused on the way it was. The Code reads: -Peace is a lie, there is only passion. -Through passion, I gain strength. -Through strength, I gain power. -Through power, I gain victory. -Through victory, my chains are broken. -The Force shall free me. While the Jedi taught their followers that love, anger or passion were forbidden, the Sith embraced the full range of human emotion; passion is what makes people powerful, and free. The original Star Wars movies clearly show that the Skywalkers don't share the belief that love is to be avoided, and it's arguable that most of humanity would relate more to the Sith's view of passion as a good thing. The first Jedi Exiles' aims to revive dead worlds may not have been something their brethren believed in, and resulted in them being cast out, but it wasn't spawned by malice.
The Jedi Were HypocritesFascist governments throughout history have proven that the denial of....unpopular progress on grounds that it challenges existing beliefs of what's "right" is one of mankind's worst habits: Galileo, for instance, was called a heretic for claiming the Sun, not the Earth, was the center of the universe. It's no secret that the Jedi oppose anything - anything - to do with the Dark Side, since nothing good ever comes from it. What is less known is that before the Galactic Republic, the galaxy was largely ruled by the Rakata race's 10,000 year Infinite Empire. Like many others, this empire was built on cutting-edge technology (like the first widely-used hyperdrives). And it was all thanks to the Dark Side. Once the Rakata empire collapsed 25,000 years prior to the films, the technology was up for grabs, with the Corellians among the first to circumvent the Dark Side components of Rakata warp drives and sell the technology wholesale. The result was helpful, so no one batted an eyelash. Transportation's one thing, but the trademark of the Jedi Order - the lightsaber - is one that could only be crafted by those in tune with the light side of the Force, right? Right. The Rakata called their version 'Forcesabers,' using the Force to channel dark energy into a solid blade. The Jedi, as they did elsewhere, saw the potential made possible through 'ways of the Dark Side,' and adapted it for their own aims. Sure the technology was used by the Rakata for conquering and domination, but if every advancement that aided warfare was seen as inherently evil, the world would be a very different place. Maybe the Jedi actually meant that 'nothing good comes from the Dark Side... anymore.'
The Jedi Helped Commit Genocide
If it's possible to bring the morality of the Jedi into question, it's in the way they treat their enemies. After the First Great Schism came to an end, and the last twelve 'Dark Jedi' surrendered, public demand for their execution ran high. Ever the merciful diplomats, the Jedi chose to spare the lives of their fallen brethren and their followers. They then proceeded to strip their former allies of their weapons and armor, boarded them onto unarmed transport ships, and sent them into Unknown Space. It's hard to say what the Jedi intended to happen to the Exiles, but when the helpless prisoners found the race of red-skinned Sith on the planet Korriban, they did what Jedi do: shared their beliefs and technology, and laid the foundations of a new empire. Old feuds die hard, so once the Sith had emerged as a suitable army for their Dark Jedi leaders - now Sith Lords - the unbelievably named Great Hyperspace War began. The Sith ultimately succumbed to infighting, and the Republic and Jedi were victorious. Clearly, their actions 1,900 years earlier hadn't worked: the Dark Jedi had survived, and now ruled over a previously-unknown race of Force-sensitive humanoids. Republic Chancellor Pultimo looked upon an enemy that no longer posed a threat, and ordered the Jedi and Republic forces to invade Sith Space and destroy any remains of the empire and its citizens. This purge - known as the Sith Holocaust - ultimately failed, leaving the survivors to take refuge on Dromund Kaas. From here they would rebuild their empire, and not rest until they had their revenge on those who had tried to exterminate them.
The Jedi Defended a Corrupt System
As so many galaxy-wide armed conflicts do, the Clone Wars all started with the passing of a Financial Reform bill. Well, attempted passing. You see, this is the part that gets glossed over in the clearly pro-Jedi films, giving the impressions that the Separatists were simply bad guys. The truth is: the commercially powerful systems of the galaxy were only after removal of corruption in the Senate, and government deregulation in the name of capitalistic growth. Those wishes could be cast in a greedy or antidemocratic light, but they're also the desires that shaped the creation of the western world. In other words, not inherently evil. The taxation and corruption of the Senate from top to bottom pushed the larger corporations not to revolt, but introduce new financial reform to protect their interests. Before a vote could take place, the Senator representing the Commonality of trade planets was assassinated by a bribed Senate guard (apparently they weren't kidding about corruption). Those who sent the assassin got their wish, and the vote was cancelled. Understandably, this was the last straw. The Commonality broke off from the corrupt body and formed the Confederacy of Independent Systems. Political movements are usually bigger than they're made out to be their opponents. so while the films depicted the group as a table full of villainous characters, the Separatist Confederacy was made up of over eight galactic governments, dozens of Republic Senators, and spanned over 10,000 star systems. The Jedi and Republic didn't even formally recognize the group's existence, choosing instead to defend the corrupt government, and rather than address the Separatist concerns, simply wipe them out.
The Jedi Betrayed Their Own Beliefs
Have a look, if you will, at the stated beliefs of the Jedi Code around the time of Episode 1 - The Phantom Menace: -Jedi are the guardians of peace in the galaxy. -Jedi use their powers to defend and protect, never to attack others. -Jedi respect all life, in any form. -Jedi serve others rather than ruling over them, for the good of the galaxy. -Jedi seek to improve themselves through knowledge and training. Of course, the Force-wielding, telekinetic, mind-controlling monks weren't always so docile. When the Jedi put an end to the New Sith Wars 1,000 years before the films, they had grown to be so militarized that their beliefs were being jeopardized. As recognition of this danger the Ruusan Reformation took place, restructuring the Republic and disbanding the Jedi's army and navy, as well as restricting their influence. This meant no longer sporting armor or military rank, and serving the Senate, not their own hierarchy. Rather than weakening the galactic government, having the Jedi to defend freedom and serve democracy ushered in the 'Golden Age of the Old Republic.' The films are set 1,000 years later - enough time for the Jedi to have shifted from realizing their religious order should only be used to defend, not lead the Republic to claiming that they knew better. George Lucas could have at least included a scene where Mace Windu or Yoda debated the idea of instantly becoming generals, betraying their code and undoing legislation that brought a millenium of peace (fun fact: Luke Skywalker later removed the line about "never attacking others").