Oh! Oh oh oh oh! Me! Pick me! Long ago, someone on here asked this same question. I gave a reason or two, then said, "Just read the books." His response was something along the lines of, "If it has to be explained in the books, then it doesn't count." That made me angry because a lot of his counter arguments were coming from Expand Universe stuff, but I didn't want to point that out. So I just gave up.
However, I did start seriously thinking about the original trilogy, looking for examples. I found a lot of them and wrote the list on my Facebook page ages ago. Sadly, there is no 'search your posts' option, so I will have to do my best to remember it.
Let's start with the very beginning of A New Hope. Storm Troopers have taken over the ship, killing nearly everyone they find. Granted, these people were shooting back and fleeing from the 'law', so that's forgiven. And we do see that they took a few prisoner. Cut to Darth Vader. He is choking the life out of the ship's captain. He ends up snapping his neck and tossing him aside like trash. The Storm Troopers don't even look at Vader funny. This is clearly normal stuff for them; Killing unarmed prisoners in a brutal, painful death (up until the neck snap anyway) is nothing new. One point for evil.
Next we cut to the meeting between the Moffs and Tarkin. Tarkin says the old senate has been swept away and dissolved. Judging by the way Tarkin says this, I'll bet money a few of those people were literally dissolved. But that's my guess. No proof. What there is proof of is Vader choking someone because he disagrees with him and mocks him. And what does everyone do about it? Nothing. Vader continues to choke the man until he nearly dies and after Tarkin orders him to stop--letting it go on far too long to begin with--Vader acts like he's choosing to follow the wish of a child. "As you wish," he says as he casually tosses his hand back. These are not the actions of a kind person, but one who is used to crushing people for no other reason that he's mad at them. And that's ACCEPTED behavior among the Moffs because no one is horrified and demands for Vader to stop. They all get the look of, "Oh crap. Hope he doesn't do that to me next." Another evil point.
So by now, you may say that I'm just proving Vader is evil. Not so. Let's look at the Storm Troopers sent to retrieve the droids. They do some seriously questionable, and most would say down-right evil, acts. First, they slaughter an entire colony. What? When did they do this? Remember what made Luke realize the troopers were heading home? They found a Jawa sand crawler wrecked and its inhabitants slaughtered. This is pointed out to be done by Storm Troopers. Why did they kill all those beings? The Jawas didn't know about the droids, didn't know about the plans, posed no threat to the Empire, yet the Storm Troopers slaughtered every one. Evil Point.
Next, Luke gets home and we're all familiar with what he finds there: He aunt and uncle, dead. But not just dead. No, the Storm Troopers didn't line them up against a wall and shoot them. They burned them, most likely alive. Why alive? See the way they have their arms stretched out like they were in pain when they died? And even if they weren't alive, why burn the bodies? These are two farmers who live out in the middle of nowhere. They were no threat, but the Storm Troopers killed them in quite possibly one of the most painful ways possible and then burned down their home. Evil point again. Talk about spite the well.
Finally, there's the final scene with the Storm Troopers on Tatooine. Many people see them coming and get right out of the way, like they're terrified. Probably not a good sign when the civilian population is ducking out of the way of people who are supposed to be keeping law and order. However, the reason for this is made obvious when the troopers catch up to Han. No warning. No, "Excuse me sir, we need to speak with you." No nothing. What's the first order given? "Stop that ship! Blast them!" These Storm Troopers are trained to kill on sight and gather information from bodies, not live people. These are not the type of people who go around enforcing a fair and balanced democracy. These are death squads who will kill you if you so much as sneeze funny.
Alderaan. If you don't think wiping out a planet full of innocent people makes you evil, I'm scared of you. However, since we're dealing solely with movie stuff, your point is still invalid. When in the movie does it say that the rebels are using Alderaan as a base? It doesn't. The only rebel we know of from that planet is Princess Leia. The rebels are using Yavin 4 as a base, seeing as that's where most of them are at the end of the movie. Tarkin blows up an entire planet just to break the will of a prisoner. AN ENTIRE PLANET FOR ONE PERSON, who wasn't even on the planet. And no one on the Death Star--not the techs, not the troopers, not the pilots, not the guy who lined up the firing solution--so much as goes, "Oh...oops." They all knew exactly what had just happened and they're fine with it. Those that weren't probably got on the next shuttle out of there. Massive evil point.
Then there's the stuff that goes on inside the Death Star. Princess Leia is tortured, and judging by the length of that needle and the way she huddles in the corner, this is some pretty serious torture. And how does the warden of the prison cell respond when he see Chewie? "Where are you taking this...thing?" Racism isn't going to earn you any good points either, because racism leads to some seriously disturbed stuff. Two more evil points.
And that's just the first movie. Moving on to the second and third now...
In The Empire Strikes Back, Vader executes not one, but two of his own people. Why? Because they failed him. Oh, you screwed up? I'm going to choking the life out of you now. Once again, no one is surprised by this. It's just another normal day in the Empire, where being human is the only way to get a job, and will most likely get you killed by your superior because humans make mistakes.
Next we have Vader and the Storm Troopers torturing Han. Torture again. Painful torture, judging by the screams Han is letting out. And why? Why are they doing this? The Rebellion is currently scattered. Han and Leia haven't been in contact with anyone because they've been on the run since they left Hoth. That's why they go to Cloud City, so they can get a handle on things in a safe place. Nor do we even see Vader or the troopers asking Han any questions. We can only assume that Vader tortures him just for fun. Evil point.
What happens when Lando makes a city-wide announcement saying, "The Empire has taken control of the city"? Do people just go, "Oh, no big deal. They're nice. Everyone carry on like normal."? No, people instantly fly into a panic. These are not space pirates, rebels, or low-lives. These are gas miners and their families. They should have nothing to worry about, but the thought of the Empire running their city sends them screaming out the door. Meaning that there has to be a reason for their screaming. Probably because they know that Storm Troopers and the Empire aren't exactly the nice government that the Emperor would want them to believe. Evil point for proof of how the citizens of an honest city react to your arrival.
Finally, there's Return of the Jedi. By now, the viewer has already established in their mind (or at least Lucas hopes so) that the Empire is evil, so there aren't many examples of it. It's just a straight up brawl. We do see that the rebels are not racist, as they have an alien in charge of the fleet, along with an alien crew, and Lando has a co-pilot who is also an alien. In the deleted scenes, we also see there are alien starfighter pilots. But there is one example, perhaps the key to everything, in the final moments of Luke's time aboard the second Death Star:
The Emperor starts torturing Luke. He is running electricity through Luke's body, something that I can only imagine how painful it is, and he's LAUGHING while he does it. He's taking pleasure watching his victim suffer in agony before him. He's not being merciful and just killing him quickly. The Emperor is making sure that Luke suffers a horribly painful death at his own hands, and he doesn't want to miss a second of it. If the man at the top is this corrupted, twisted, sick, and downright evil, do you still think that the government he runs is nice, equal, and fair?
And that's all I have to say. Wish I had caught this topic when it was still on page one as I would like to see what people would have had to say about it. Oh well.