Killing captive enemies is one of those ethical questions that can come up within a game. You've neutralised your foe without needing to kill them, but is it okay to kill them once they're subdued? Does it matter if they're unintelligent monsters, or intelligent but evil through choice, or inherently evil beings such as demons?
The only advice we can give is that this is one of those things that each player and each character needs to think about for themselves.
Commentary by memnarch (who has not seen the movie)
Yep, arguing. Come on Chewie, shoot her already! Honestly, this is gonna turn into tea time round two at this rate. Though if it does, I also can't see how Chewie lives through this as if Zeppo gets attacked by someone else. Finn would probably be designated as "too risky" and killed as well, and I know he's not gonna kick the bucket anytime soon.
So maybe this is just going to be an exposition dump of things that would have come previously before in the movie? We haven't had a proper one of those in a while, plus it'd be one a player is actually asking for! Phasma needs something else besides the "speaks in old poems" trait anyway.
Finn: Now what do we do with her?
Zeppo: Kill her.
Finn: Kill her? What, really?
General Phasma: Fiend, I defy thee! with a calm, fixed mind, All that thou canst inflict I bid thee do.
Finn: I’m beginning to come around to it, actually.
General Phasma: How little idea you have with whom you are dealing.
Zeppo: Why don’t you tell us, then?
General Phasma: I shall! But first, an informative digression to enlighten such weak minds as yours.
Finn: Oh, can I kill her now?
Zeppo: Wait! I want to hear this!