The Mandalorian Season 2

[Aeson]

I mean, ultimately, the Force is weird. Everything in the Force happens in the now, meaning that the light/dark association of any particular action can shift from moment to moment depending on a variety of factors.

It's "weird" because you're looking at the morality of the actions themselves and failing to consider the morality of the motivations behind the actions. In striking down the Emperor at the end of his duel with Vader, Luke would be choosing to act out of fear, anger, or hate - the Emperor has not yet revealed himself to be a threat to Luke in any physical sense and there is no clear reason to think that the Emperor's death would have any influence on the outcome of the battle between Imperial and Rebel forces in the background as the Emperor for the most part appears to be an observer to the engagement, so what's Luke's immediate motivation to strike him down at the end of the duel? Hatred of what the Emperor stands for, anger over being manipulated into fighting his father, perhaps fear of what further machinations the Emperor could yet devise. Manipulating Luke into consciously choosing to take an action like this in contravention of his morals is exactly what Vader and the Emperor have been attempting to do throughout their time with Luke in the throne room - that's pretty much the entire point of the Emperor telling Luke that the Rebellion is walking into a trap and allowing Luke to witness the engagement between the Rebel and Imperial fleets was, it's part of why the Death Star superlaser's operational status was kept secret until Luke was in position to observe its effects, it's the primary reason for the Emperor to assure Luke that he's unarmed even as he encourages Luke to take up his lightsaber and strike him down, it's why Vader prods Luke over his failure to hide his relationship to Leia and suggests that Leia would be the next target for corruption if Luke refuses to fall, and it's why the Emperor speaks up at the end of the duel to push Luke to strike Vader down, because he doesn't really want Luke to kill Vader in the heat of the moment - he wants Luke to consciously set aside whatever remained of his earlier scruples and choose to kill Vader, now that Luke's been provoked into breaking his earlier moral restraint and in so doing has beaten Vader down and disarmed him.