I would say that radical individualism goes back to Locke, who made liberty the predicate of justice based on the idea of human beings existing as isolated individuals. In reality, humans have always been social beings.

Nonetheless, Liberal thought has been infected ever since with the notion that Lockean individualism is necessary to justify maximizing liberty in society. In reality, all that is necessary for co-existing human beings to maximize liberty is for us to engage in mutual respect (of a basic kind: taking one another into account) — which, as this book argues, we are innately prone to do. Otherwise, we would not be social beings. "Re-thinking Individualism" (here in Medium)