Other mistake: During the final confrontation with Vader on the Death Star, Luke bashes a catwalk railing with his light saber several times, but there are no burns, marks, or indentations on it at all. Considering the power of a light saber (Qui Gon melted a steel door in Phantom Menace), some damage should be visible. Only when he hacks off Vader's hand does the light saber slice through the rail.
Continuity mistake: When the Emperor is torturing Luke, in the shot after Luke groans, "Father, please", Vader and the Emperor are standing further away from each other than in the previous and following shots where both are visible. (01:51:20)
Other mistake: When the ground battle on Endor begins, Leia runs to the bunker, and as the doors close, she fires a shot. In the original version of the movie, the blaster smokes, but no laser beam comes out of it and no sound is heard (do not confuse this with the sound of the doors closing). In the Special Edition, the sound has been added, but the laser is still missing. (01:38:05)
Other mistake: In the original cinema release, one of the subtitles for Jabba's conversation is incorrectly spelled - 'there will be no bargin'. This was corrected for the video release.
Continuity mistake: After Leia removes her helmet in Jabba's palace, her hair changes on the right side of her head, depending on the camera angle.
Deliberate mistake: The shots of the prisoner skiff during the transport to the Sarlacc Pit are reversed. This can, for example, be seen as Chewie's bandolier is on the wrong side, and that Han's shirt is overlaying the wrong way.
Continuity mistake: As Boba Fett nods to the disguised Leia after the latter turns off the thermal detonator, his costume is reversed due to the negative being flipped. The easiest part of his costume to see this on is his antenna, which is on the left-hand side of his head, whereas normally it would be on his right.
Continuity mistake: When Wicket sits down next to Leia on the log, he's holding his spear straight up. In the next shot, it is pointing downwards. (01:01:35)
Continuity mistake: In the first shot of the hologram of Endor and the Death Star, the Death Star orbits Endor in an counter-clockwise direction. In the subsequent shots, the Death Star orbits in a clockwise direction.
Revealing mistake: Look carefully at the close-ups of C3PO's waste where the exposed wires are. You can tell it's fake wiring on top of a black suit which is particularly noticeable when the actor inside the costume as his stomach is moving when he has to breathe.
Revealing mistake: When Luke is fighting on a skiff, he kicks one of Jabba's men in the head, causing him to fall off. Luke's foot doesn't make any contact with the person. (00:33:48)
Continuity mistake: In the Special Edition, Sy Snootles (the lead singer of Jabba's band) is CGI, but in the original version, she was a puppet, looking a bit differently. In the first shot of the band sequence, you can see the old puppet singing on the stage. (00:11:50)
Continuity mistake: After Vader's shuttle lands on Endor, as the AT-AT is walking towards one of the ramps, you can see that the ramps are connected right next to the lift, under the landing pad. But when Vader exits the lift, there's a circular platform going around the lift, which wasn't there in the previous shots. (01:19:40)
Other mistake: When Vader's shuttle lands on the forest moon of Endor, an Imperial AT-AT walks near the landing pad. There's a strange shadow that keeps appearing and disappearing on one of its leg. Maybe the shadow of the puppeteers?
Visible crew/equipment: When C-3PO And R2-D2 come up to Jabba's palace in the beginning of the movie, in the close-up, you see overhead stagelights in the reflection of C-3PO's head.
Revealing mistake: Widescreen version only: After Luke cuts off Vader's hand, the Emperor says, "Now, fulfill your destiny, and take your father's place at my side." In the next shot, Luke's lightsaber blade goes through the railing, without damaging it. (01:49:15)
Continuity mistake: When Lando is dangling from a rope over the Saarlac pit, he keeps moving up and down the rope between shots.
Revealing mistake: During the lightsaber duel, Vader throws his at Luke. The catwalk behind Luke explodes, but if you watch closely there are two explosions: one some inches over where the lightsaber actually hits and one far on the left.
Continuity mistake: When R2-D2 is assigned to his duties in Jabba's palace, another droid (EV-9D9) says, "But you'll soon learn some respect." and her arm is in a different position from the previous shot. In the following shot, her arm is in its original position. (00:11:10)
Other mistake: When Leia gets on the speeder bike, it starts before she pushes the button.
Answer: Darth: "Obi-Wan once thought as you do. You don't know the power of the dark side. I must obey my master." It's implied that the dark side is intoxicating, once you totally give in to the dark side it has a hold on you, and appeals to morality and rationalization are useless against your lust for its power. (On a symbolic level, the dark side is a metaphor for vice. Darth Vader is an addict and abusive parent. It's actually funny how many scenes still make sense if you replace "the dark side" with "the bottle" or similar).
TonyPH
If we bring the prequels into it, it's one of the criticisms of those films that they only make the question of how much Anakin is a "true believer" more confusing. But it stands to reason that at first Anakin may feel vindicated in his resentment toward the Jedi. Later on, Vader may not feel that as strongly, but by then his anger has turned toward himself for failing to save Padme. He may feel that a man as terrible as he does not deserve to be "rescued" from the dark side, leading to a feedback loop where he only gets further enamored with its power and does more evil things which causes him to hate himself even more, and so it goes.
TonyPH