“It fades. I want to say it goes away forever, but I’d be lying”. A key difference in Andor between the two sides when it comes to choosing to kill for the cause…
There are a couple of interesting later echoes from one of my favourite sequences in 2.04, when Cassian and Bix discuss their most recent (off-screen) mission - where Cassian killed an Imperial soldier apparently just because he saw Bix’s face.
Bix’s nightmare of the tortured dead soldier ^
Bix is clearly so haunted by what happened that it’s crept into her PTSD-fuelled recurring nightmares about Doctor Gorst. In the one at the start of 2.04 where she sleep walks and appears to encounter Gorst torturing the soldier, we see not only his corpse in the chair but also a brief glimpse of what appears to be part of the uniform he was wearing. It’s the helmet and armour of an Imperial Security Trooper - and specificially of the kind we have seen already during the riot on Ferrix and that we’ll soon see again - on Palmo Plaza.
Imperial security troopers on Ferrix ^
On Ghorman, we see how exactly how young the cadets are. The somewhat sympathetic Sergeant Bloy clearly feels protective of them, reacting with horror when Captain Kaido orders him to get them patrolling into the crowd. “They’re green, sir. They’re useless”. Kaido simply says: “I see Imperial uniforms, Sergeant.” So they are sent out into Palmo square. In the still here, one of them can be seen clearly just before his riot gear visor slips down over his face. (Possibly an accident, but a great choice to leave it in the edit if so)
^ Under orders from Kaido, Bloy prepares his “green” cadets for facing the crowd in Palmo Plaza. He has no idea they will be lambs to the slaughter. In the next second here, that cadet’s visor slips down.
Cassian and Bix are both affected by the killing of that one soldier, even though both of them have killed before. From the visuals and dialogue we can probably conclude that he was as young as these troopers on Ghorman, who Bloy couldn’t even bring himself to describe as ‘men’. Bix refers to the soldier at one point as a ‘boy’. The Gorst figure, presumably a manifestation of Bix’s own tortured conscience, taunts her with the details. “His family will never find him” suggests his body was dumped somewhere remote or completely destroyed. “Not much of a soldier, was he?” suggests his youth and also that he probably died ignobly - begging for his life, maybe even crying or trying to run away. “I know you wanted him to live” suggests that Bix possibly argued about it with Cassian at the time.
^ As she cleans their weapons Bix confronts Cassian again over the killing: “ I can’t stop seeing his face”.
Later in the episode, the couple debate what happened, with Cassian attempting to be cold and detached about it - and Bix trying her hardest to move on too, but it’s clearly deeply troubled her. Particularly the idea that she is the reason for the killing: “You didn’t kill that boy because we are at war, you killed him because he saw my face!” Cassian’s defensiveness causes him to repeat himself: “Hey, he was a threat. He was a soldier. Bix, you put on the uniform, you take your chances”… and a little later: “He was a soldier. He was a threat. He was an Imperial threat. You and I are here now because he’s dead. It had to be done.”
“It had to be done” is also what Kleya will later say to Vel, concerning what she did for Luthen. Vel wryly responds: “It gets tiring saying that, doesn’t it.”
^ Vel can see how much Kleya is in shock here over causing another necessary death… that of Luthen.
This is one main difference between the rebels and the Empire. Both do ‘terrible things’ for the fight. But the rebels feel the horrible weight of it, of taking lives even when it was a ‘necessary’ choice. “It fades,” Cassian eventually concedes to Bix after she tells him that she can’t stop seeing the soldier’s face. “I want to say it goes away forever but I’d be lying.”
While the rebels are beating themselves up in this way, the higher echelons of the Empire spares its soldiers no thought at all. On Kaido’s orders, the sniper coldly selects one of these young cadets, one of these “boys”, and deliberately shoots him dead in a false flag move to kickstart the Ghorman Massacre. The cadets become as much victims as the crowd, and of course this will play into the propaganda on the Imperial news. Exactly as designed by Krennic, and Palpatine. 
Will it make Kaido feel uncomfortable? No. His concern is that he has “a comfortable ride home”.
It says it all about the difference, really.