Good post.
Further points for consideration. From an antagonist perspective, killing someone is often the only way to actually remain "safe". Or "Safest" out of all of the possible alternatives. A majority of characters tend to taddle the moment they're released, even if under some form of threat. Keeping hostages is incredibly costly and basically removes your freedom as an antag, because you have to monitor the hostage, and hostages aren't mobile. Etc. So really, if you get caught doing something naughty, very quickly, aggressively, and violently nuking whoever saw you is the best way to remain safe. Sure, someone's gonna see a murder, but they won't have a clue as to who did it. At least, not initially. "Violence of action" is a very useful principle to adhere to while playing antagonist in SS13, including on Aurora.
Killing someone in such scenarios obviously will not really "offer" any RP to the unfortunate victim. But the idea is that keeping the antagonist alive and safe will allow them to continue affecting the round. And the more an antagonist can affect the round, the more eventful the round is. Ideally, anyways. Obviously many things can happen. Security can shut them down later, they might fuck up, their plan might end up failing, whatever. But such is life.
With regards to what could be done to amend the situation. Here's a thought. Even if the staff end up ruling in favor of an antag from the player complaints, ahelps, etc. that get generated from legitimate killing of characters, there's a considerable amount of mental stress from simply being involved in such activities, moreso as the "target". So perhaps more decisive dismissal, without even touching the implicated player, would benefit the general situation? It would make the antagonist players feel safer, since they no longer get pinged about everything.
Also, anonymizing antagonists further would possibly help. 🤔