Vladius said:
No, it's just more subtle. Can't the audience figure it out on their own that killing the Emperor is part of the victory, and leads to the celebration across the galaxy later on? Just like how people with the Force being angry does not mean they suddenly get yellow eyes, but it's still clear that they're angry and that the Force intensifies their feelings.
He's persuading him through multiple angles - through vengeance and anger, through exploiting his compassion ("they do you credit, but they could be made to serve the Emperor,") through his desire for power.
You're acting like all these things come out of left field with no precedent, when Obi Wan and Yoda told Luke already. They told him to confront Vader, something he already struggled with - now that he has a reason to be angry at Vader, he snaps. He had to hide in order to avoid fighting him. You can see the concern and stress on his face, he feels overwhelmed psychologically from the weight of the Emperor and Vader tempting him, like Frodo with the Ring. It's clearly implied that even if there is no specific goal that Luke would achieve, the Emperor's powers of persuasion are powerful enough to defy reason.
Sorry....but saying the emperor's powers of persuasion are powerful enough to defy reason as a way to explain lack of character motivation is 10x the cop-out of giving someone yellow eyes to indicate they're evil in my book.
It does come out of left field for me, because the fact that he's had time to steel himself and he's been told by everyone how conniving palpatine is and to not underestimate him means that palpatine needs to have a pretty big ace up his sleeve to get to him. He does, in fact, have such an ace....but he plays it totally wrong in my view to have any reasonable tension in the scene.
He should have played up on Luke's compassion towards his friends and his desire to save them (mirroring anakin's fall more), trying to convince him to give in to temptation....to do just a little evil to do a greater good.
Instead he pretty much barks about how Luke has already fallen and just doesn't realize it yet, to give into his anger towards palpatine because there is no hope left already, and to strike in vengeance and turn to darkness.