i took a class in college about exactly this, basically the thing most disaster movies get wrong is that humans everywhere generally stick together and cooperate during emergencies, with the exception of places with pre-existing racial/ethnic conflicts in which case the racists will start killing. in pretty much every scenario its better to have extra hands/more expertise/trading partners, if there is literally no supplies except what you can steal from bunkers you simply aren't going to last very long no matter what you do.

also like where tf do they get the food to feed everyone in mad max, its not like their desert apocalypse villages are surrounded by miles of lush irrigated farmland or anything. fiction in general just has no comprehension of how much space and resources and effort it takes to grow enough food to feed even small populations.

killing people won't magically make corn grow out of the blasted soot-covered radioactive nuclear apocalypse soil, but keeping them around to shit out free fertilizer will help at least.