This short story places us in a terrifying future world where life is so controlled and based on fear and surveillance that nobody leaves there house after a certain time at night. The only man who is brave enough to do so is the protaganist of this story, Leonard Mead, who braves the squads of dogs that range the streets of this controlled city at night. Even though this society has seen a massive drop in crime, so much so that there is only one police car for three million people, this attitude continues, so that when Leonard Mead is stopped by the police car they take him in for "Regressive Tendencies." When he says to the police that he walks "for air, and to see, and just to walk," this is not accepted as a specific purpose, and he is arrested. Bradbury presents us with a society that has become isolated from itself, each other and nature.
Therefore a good thesis statement might be:
In a strictly controlled futuristic world dominated by surveillance and media, Bradbury shows the perils of forgetting our humanity in the fate of Leonard Mead.
This thesis statement would allow you to talk about what impression of humanity we are given and the way that at night they are said to never go out, but just watch television, sitting "like the dead." Any human impulse to go out and wander without purpose is regarded as suspicious.