Here's how the irony works:
* Regressive: The word suggests a movement backward, a decline, a return to a less developed state. In the context of the story, the Center implies that walking is somehow a "primitive" or "undesirable" behavior.
* The Pedestrian: Mead is walking, an activity that was once common but has become increasingly rare in a future where technology has taken over. This suggests that the Center views walking as a "regression" from the advanced technological society.
* Irony: The true irony lies in the fact that walking is not a backward or undesirable activity. It's a healthy, natural, and enjoyable way to experience the world. The Center's perspective is skewed, viewing Mead's harmless activity as something to be studied and potentially "cured."
By labeling Mead's simple act of walking as "regressive," the story highlights the chilling nature of the society. They are using technology to control and normalize their lives, and those who choose to engage in a simple, natural activity are seen as deviant. The irony points out the absurdity and danger of this society's values.