One of the clearest themes in horror, and other genres besides, is pointing out human cruelty. The desire to stay alive in a zombie apocalypse leads some people to sacrifice others so they can live (usually rich and rude jerks we don’t care about living anyway). One of my favourite Twilight Zone episodes is The Shelter, where people do ask ‘Why should your family live while mine dies?’
In Zombies, Vampires and Philosophy, Leah Murray refers to Thomas Hobbes claim that life in a “state of nature”, without government or authority, is “solitary, poor, nasty, brutish and short” . Murray extends this to the zombie apocalypse, looking at Romero’s Dead series. In thinking about recent battlegrounds, you could go further and apply this to jerks on the inernet – with anonymity and seeming no authority or law, people are free to call you whatever negative terms they can think of (although I do think ‘baddie’ is a stupid term).
Hiding away food, weapons, information is fairly common – especially outside of horror. But there are other examples of human cruelty that is not against each other. Cruelty against weak/helpless zombies is common, usually red necks picking them off, blowing them up, stringing them up and using them as target practise. Admittedly, this could just be a reflection of what could be our cruelty to each other if we had anarchy.
There’s nothing in the world I love like a person who likes and is kind to animals, especially my cat. There are quite a few heroes in the zombpocalypse who still look after animals and share meager stores with them (non-zombiepocalypses too!). Human cruelty is seen in so many ways and with varying levels of severity. Some see horse jumping as cruelty. Dog fights are definitely cruel. I forget where it’s from, whether academic or fiction, but I remember a saying that our civilisations worth is based upon how we treat our smallest, our weakest.