A fear about technology is that humans will invent something that will affect the past or the future.
The science fiction story “A Sound of Thunder” explores the idea of the “Butterfly Effect,” the concept that a small choice can make a big difference. In this story, a company has a time machine that it hires out to wealthy men who want to go hunting. You can go back in time to hunt dinosaurs.
As exciting as that might sound, there are potential dangers. It is a common fear involving time travel that going back into the past will somehow change the future.
"We don't want to change the Future. We don't belong here in the Past. …. A Time Machine is finicky business. Not knowing it, we might kill an important animal, a small bird, a roach, a flower even, thus destroying an important link in a growing species."
The time machine company, Time Safari, is aware that there could be potential drawbacks to traveling in time. They don’t want to affect the future by messing things up in the past. This is a common fear that Bradbury draws on. If one small event in the present can affect the future, then any change to the past must make a huge impact.