[Well, I like to think I'm a non-lunatic, when I'm having a good day. But I might be speaking only for myself.]
"The non-lunatic right holds that market economies are indeed macroeconomically unstable but they can be balanced by minimal interventions in aggregate variables: that is, by assigning the central bank the [task] of controlling the money supply in order to make Say’s Law true in practice even though it is false in theory." [He actually says "cost", not "task", but I think that was a typo.]
The bit about wanting to make Say's Law true in practice even though it is false in theory is fine. Both non-lunatic left and non-lunatic right want something like that.
It's the bit about market economies being macroeconomically unstable that is....not even wrong. It's confused.