Good thing that most people tend to judge you for killing a given finite number of people, rather than based on the percentage of the population. That is to say, If you kill one random person in China, you're generally considered just as much a murderer as if you kill one random person in Luxembourg
I'm not sure if that's necessarily true. For one thing, thanks to ✨racism✨, who you kill will influence how you're viewed. And if you kill enough people, I think it often causes people to view the event less personally ("one person is a tragedy, a million is a statistic"). Of course, that also depends on how you kill them. Killing one innocent looking civilian with a trolley will go over a lot worse than sending a million soldiers to die in a war (no matter how pointless or wrong the war was).
Also, if there's an infinite amount of people on the tracks and you have infinite time, you could kill a (countably) infinite number of people. If killing one person is a bit frowned on, klling tens makes you a monster and killing millions makes you whatever Hitler, Stalin and Mao were, not sure what they'd call someone who killed ℵ0 people