There's quite a difference between actually killing somebody and allowing them to kill themselves in a painless/peaceful manner - e.g. providing them access to drugs/devices that they have to choose to use themselves.
Yet it reflects the natural reaction of not deliberately killing someone for the greater good, because people judge that more evil than the neutral position of not intervening.
Also, if you don't intervene, you don't have to answer to the police about why you deliberately killed a man. Murder is murder, even if your intentions were good.
If you know that people will die, but are simply indifferent to it, the difference between that and actively wishing to murder is at least arguably academic. You are killing people with your choices in either case.
Morally, you're also killing someone with no intent on harming you who isn't an immediate threat. Sure, its not quite straightforwardly wrong, but it sure isn't right.
If I'd pay a hit-man to kill a donor I wouldn't get away with it, despite the urgency. If I knowingly visit a country who kills people for donation I am an accomplice. Where I come from this has the same term as the deed itself.
Outside being attacked you can't kill people for self-preservation.
Trying to kill someone because they beat you in a game is significantly more evil than trying to kill someone because you mistakenly believed they posed a threat to human life.
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