Most of the violence in the movie are... (spoilers)
The violence in the movie are mostly directed between members of the lower class. It mirror real life that people do not have class consciousness and the lower class fight among themselves vs. against the upper class.
The Kim family has no ill will against the Park family. They just want to be "parasites" off of their wealth and extract as much as they can. However, when another family show up on the scene, they're competitors so they receive most of the violence.