To me, the characters within the film fall directly into line with how characters stereo-typically act when they find themselves in a slasher story. They are brash, young people who give little thought to the future and are just trying to have a good time. They react, for the most part, stupidly to the threat of Johnny. Thus they become fodder for Johnny and the natural violence found in the world.
The key to the entire movie is what Kris decides to do with Johnny's locket. For the last act the film beings building to the typical slasher climax, a big, bruising battle between the Goliath and the fierce, nothing left to lose Final Girl. However, instead of continuing to thoughtlessly participate in the story that's been told many, many times, Kris does the intelligent thing: she simply lets Johnny have what he wants. She let's nature be. She acts in good faith. And that's enough to satiate Johnny. He does not follow her. He does not continue on his violent impulsive path. His own rightful property is returned and nature becomes quiet once more. The woman in the pickup truck tells the story of her brother that re-enforces the idea of nature having violent tendencies that only let up when we do the smart thing and act against our own human retaliatory programming.
There's also heavy signs of Kris suffering trauma after the incident, being so paranoid Johnny is still after her. Suggesting to me that perhaps Kris/the audience has done so much damage already that the scars will remain even if we start doing the right things and acting in good faith.
That's my interpretation. In a Violent Nature is great because I do think it IS open to lots of interpretations though!