[This could be seen as an extremely rough partial draft of a post I've been meaning to write about the role negative information (what wasn't said, what didn't happen) plays in the interpretation of fiction. This is the first Death Star, in the original Star Wars.]
Its essentially the same mechanism that lets us not care when Luke blows up the Death Star and kills everyone on it- they aren't "real," they're just props to showcase the hero.
No. No, no, no. No.
That is not why blowing up the Death Star is considered an acceptable, even laudable, act of self defense.
I've been meaning to write an article on this for years, maybe someday I'll get around to it, but for now the short version.
When the Death Star is built it's an idea. When it first sets sail it's thought of as a deterrent. This ultimate power will cause the rebellion to collapse due to fear. That's what the higher ups say. When it is planned to be used against the planet with the Rebel base it becomes an overpowered weapon of war.
Then it blows up Alderaan. An unarmed non-rebellious planet with no strategic significance.
When the order was given there was no secret as to why, there were plenty of witnesses none of them sworn to secrecy. The goal was to publicly kill an entire planet full of innocent people to anoint the Death Star as a weapon of terror. Not a theoretical deterrent. An actual engine of mass murder whose purpose was to kill innocents until the other side backed down.
In that moment everything changed. Before then the Death Star was like the USSR's nuclear arsenal: there was no solid evidence it would actually be used in anything outside testing and demonstration. After that moment it was unmistakably a tool whose intended use was the annihilation of civilian populations.
Everything changed except for one thing: the absolute loyalty of everyone on the Death Star.
We don't shed a tear for them not because of what they are, but because of what they aren't. Not because of what they do, but because of what they don't do.
When the order was given no one tried to stop it. Not on the bridge, not in weapons control, not anywhere. With their part in the deaths of all those on Alderaan still on their hands no one tried to do anything. The imperials walk unaccosted through the halls. The engines run, The weapon charges up.
We don't see Tarkin running through the halls with his loyal bodyguards as they dodge incoming fire. We don't see a stormtrooper charging the loyalists in a desperate attempt to reach the weapons controls screaming, "For Alderaan!" We don't see the detention area being filled with those who tried to object to the whole mass murder thing. We don't see Vader tightening up security because of the threat of mutiny, we don't see the insurgent stormtroopers and TIE pilots and technicians and cafeteria workers getting together for a strategy meeting in a barricaded part of the Death Star.
We don't see an engineer crawling through maintaince tunnels in the hopes he can get to, and disable, the power source for the weapon before it can be fired again. We don't see someone saying that the trip to Yavin IV will take longer because sabotage has the engines running at less than peak efficiency.
We don't see threats used to keep the crew in line. We don't see nervousness that the person sitting next to a given imperial might be part of the mutiny waiting for the ideal moment to strike.
We don't see turbolasers being turned against the station itself by their operators. We don't see computer technicians trying to do whatever they can* to make Alderaan not happen again. We don't hear anyone saying, "Never again."
We don't see the resistance struggling to the last moment to stop that damned gun from going off. We never hear the battle cry, "Remember Alderaan!" We don't hear Tarkin say, "Evacuate? What the hell do you think I've been trying to do for the last twelve hours? We're cut off from the hangar bays!"
We don't see so much as a single person being relieved of command for refusing to obey orders. We don't see so much as a single person expressing moral qualms.
We don't see resistance. We don't see steps taken to thwart resistance.
What we do see is business as usual with all evidence supporting the idea that every single person there is a willing participant in mass murder. And that's why not a lot of grief is had for them. Because by their inaction they condone and moreover support mass murder. Vader and Tarkin couldn't run the station by themselves, and there's no evidence anyone who helped them do it was under any kind of coercion.
By their choices we condemn them, because they had the power to save billions, and they chose instead to be loyal mass murderers. Set pieces would not be judged so harshly. The population of Alderaan was composed of set pieces, yet their deaths are seen as tragic. Because they didn't go along with mass murder.
Now imagine if it had been slightly different, what if the Death Star were mostly populated by slaves? Or what if the imperials onboard had abducted people to be their mates. Or what if there were even a hint that those affected by the blowing up of the Death Star weren't there of their own free will?
Well that would change everything. The Death Star would probably still need to go (though a less than loyal population might open the door to other options besides kill everyone) but the ending would be much more down, and anyone who even thought about gloating would be clearly evil.
* "She doesn't even have access to the firing codes, she works on the guidance system." He says with far too much arrogance and not nearly enough respect.
There was a follow up post after it was suggested that the morality was simpler:
Fandom [...] has come up with these arguments. But they're a tiny minority of the people who have seen Star Wars. Jane Moviegoer isn't thinking about that.
Your explanation still ascribes moral agency to the people on the Death Star- they're people who made bad choices. [...] Bad Guys go Boom because that's what happens to Bad Guys. And we know they're bad because they blew up a planet and killed Obi-Wan.
Actually, that's not from fandom, unless I am fandom all by myself. That's from something I was planning to write in on an entirely unrelated to Star Wars topic as an example of how common and necessary it is t o make judgments on what doesn't happen. It may not even be occurring on a conscious level, but how we interpret things depends very much on what we don't see.
Seriously, why are they bad guys?
[Added] To clarify, I'm not asking for a detailed moral argument. You started your explanation of typical experience from a premise of them already being bad guys, how does one reach that point? [/added]
It's not the armor. Han and Luke wore that.
It's not the affiliation, Leia was part of the imperial government.
It's not the location, every single one of the main characters was on that battle station at some point.
Them being badguys is entirely about negative information: None of them take off a helmet and say, "I'm John Watertreader, I'm here to rescue you." None of them get denounced by Darth Vader saying, "You are part of the Rebel Alliance and a spy." None of them do anything to resist.
With the exception of those tiny few directly involved in shooting at something (planets, ships, people), those non-actions are the only things that separate those on the Death Star when it explodes from the heroes.
Whether people are aware of it or not, they're judging those characters on what the characters didn't do.