2015 cat army got fired at by some humans

My friends and I were running through a forest, all six of us, running back to our camp, when we heard a noise and something whizzed past our heads. Now this was my friends forest so no one else should be in it except his family. So I get up and not expecting the slingshot pellet that got shot at my eye. I was lucky enough to hear it and block it with my had, and it bounced off right hand index finger knuckle and is now only starting to heal. I yelled and we heard people running. 2 or 3 of us ran after them but got stuck around some thick and thorny bushes. We suspect people were in this forest which was our place that we felt we could stay. It was on my friends property and clearly says so around the fences. We found the signs ripped off and a slingshot pellet on the ground.

Why are people so destructive?