Brad DeLong speaks at a Cato event

Here is the closing part of his summary:

One way to understand Keynes's General Theory is that Say's Law is
false in theory but that we can build the running code for limited,
strategic interventions that will make Say's Law roughly true in
practice. The modern American liberal economist's view of
libertarianism is much the same: libertarianism is false in theory, but
it is very much worth figuring out a set of limited, strategic
interventions that will make the libertarian promises roughly true in
practice.

Here is much more.