I hear you, but my foolish hope is that most people are either too decent or lazy to go around killing and stealing. I know every piece of post apocalyptic media swears otherwise...
It wouldn't be most people. If you had 100 people, 99% were good people but that one person has a gun and is willing to fight and steal from others, then all 99 are in danger.
And by post apocalyptic media, you mean the news? That's how people react. People are evil and we live in a fallen world.