(In before the guy that comes up with the idea for a scifi movie in which hunters go back in time and hunt dinosaurs and become the real reason dinosaurs become extinct.)
That is essentially a story in IIRC, one of Ray Bradburys collections. You go back and hunt dinosaurs that are just about to die naturally (so as to not screw up the time line). One of the characters falls off the anti-grav walkways and when the crew returns to find the world a totalitarian dystopia, they see that guy smashed a butterfly...