<blockquote>darklordoftech said:<blockquote>
Easterhay said:
What? By striking down Vader in anger, you're saying that those means would achieve the end of the Emperor and his empire. And I'm saying you're wrong, based on... well, take your pick, really, from various lines of dialogue throughout the films about striking out in anger and using your powers for attack, not knowledge or defence.
</blockquote>
Those means could fail to bring down Palpatine and the Empire, but neither would those means lead to Luke joining Palpatine. </blockquote> 
The Emperor was clairvoyant, and (up until the end) everything proceeded exactly as he had foreseen. If he said striking down Vader would complete Luke's journey to the Dark Side and subject him to the Emperor's will, that's what would happen. How Luke would get to that point is an interesting creative exercise, but it is not necessary to work it out to understand Return of the Jedi. A wizard did it.

(If you want to engage in that interesting creative exercise, an important thing to remember is that Luke was never really a loyal Rebel and didn't profess sophisticated or deep-seated political leanings. He joined the Rebel Alliance because his application to the (Imperial?) Academy had been delayed and because Vader's forces killed his family. He abandoned the Rebel Alliance because a ghost told him to, stealing an X-wing in the process, and went on a mystical quest to become a great warrior instead of fulfilling his duties during a time of great peril. Had he killed Vader at Endor, he would have avenged himself upon the killer of his aunt and uncle, proven himself a great warrior, attained sufficient power to (perhaps) effect reforms to the more objectionable aspects of the Imperial system, and he'd have more rank and prestige than he ever did in the Rebel Alliance. Tellingly, when Luke rejected this offer, he did so as a Jedi. That is why the Emperor had to break his adherence to the Jedi creed.)