James taking out four strangers with his shotgun and an axe.
Mary smashing Grace's face in.
Zoey killing the Polite Stranger.
The homeless guy saving the family from being killed by the evil neighbors
The Sanders are hated by their neighbors for their greater wealth and (allegedly) acting like they're better than everyone else. In the end, when the Sanders have every right to Pay Evil unto Evil, they refuse to engage in the Purge and in doing so prove they're better after all. And the scumbag neighbors now have to live knowing it.