I think calling Mr. Leonard Mead by his complete name indicates two things. First, Bradbury may be pointing out that by using his full name, Mead is an individual in a world where everyone is the same. Mead does not stay at home and plant himself in front of the television like other citizens in this society. Instead, he wanders the streets at night enjoying the sites and fresh air. At the end of the story it is Mead’s house that is lit up, unlike his neighbor’s house that are dark. Again, this shows him to be an individual.
Another reason his complete name is used could be to show how the world in which he live in impersonal. It is very formal to call someone “Mr.” with his full name. Mead is not seen as an individual, but as a rebel who needs to be taken to the nearest psychiatric hospital for his “bizarre” behavior of walking. The police car doesn’t give Mead time to explain himself, and it just assumes that he is insane. No personal human connection is made between the robotic police car and Meade.
The reasons are an oxymoron and contradict each other, a unique message by Bradbury.