Two Issues

There are two distinct issues here:

Is unemployment a symptom of excess supply?

Keynesian economists had assumed that it was, but New Classical economists say no -- unemployment is determined by supply equal to demand in the market for job search.

Is unemployment a social problem?

Keynesians had held that it was. Seeing unemployment as an excess supply of labor, the Keynesian view was that the unemployed person's capacity for labor was simply a resource going to waste. In that sense, unemployment would be a social problem. In the New Classical view, some unemployment is efficient. Job search, in itself, is not a social problem but is necessary. But while a certain amount of job search is efficient, we might find that we have more than the efficient amount of job search -- too much unemployment -- and since that would be inefficient by definition, that might be thought of as a social problem.

A New Classical Prescription