What is Ray Bradbury's agenda with A Sound of Thunder?
One primary element which comes out of Bradbury's short story is the idea that there are implications to all of individual actions. By merely falling off of the path, the story reveals drastic consequences, unforeseen by something so minute. In a time period where the Cold War and preoccupation with control, action, and domination, Bradbury's story helps to reveal how there is little, if any, learning curve when human action is combined with severely potent weapons of destruction. Bradbury seeks to bring forth the idea that individuals cannot see past their own decisions and action, and thus freedom has to be exercised in a prudent and cautious manner.
I believe that what Bradbury is trying to do with this short story is to tell us how easily things in our lives can change and how easily things could have been different.
In this story, he imagines a scenario where one person, millions of years ago, steps on some grass. Somehow, that single action ends up causing a major change in the history of the United States. It ends up causing a different history, one in which the US seems much more like an authoritarian state.
So I think he is trying to warn us about how fragile our reality is and how easily our own way of life could be destroyed.