when you're the only person who keeps living through the time loop, the people around you cease to be people and become mere characters. your treatment of them doesn't matter because they're not real and they won't remember. the only way to give anything meaning is to end the loop; their actions don't affect the loop and therefore are meaningless. you're the only one who has the ability to change the future, so anything you do in service of that goal is justified.

but. kim dojka looks at yoo joonghyuk and says no, actually, these characters are people. whether they remember or not is beside the point because they are real right now. and you don't give your life meaning by achieving some accomplishment that retroactively makes everything that came before worth it - you give your life meaning in the living of it.