Those who advocate that the Fed target monetary aggregates, usually argue that the Fed should not alter its monetary targets in response to temporary...

Those who advocate that the Fed target monetary aggregates, usually argue that the Fed should not alter its monetary targets in response to temporary changes in macroeconomic conditions, yet those who advocate interest rate targeting never recommend that the Fed maintain a constant federal funds rate target. Why not? (What's the potential danger of maintaining a rigid interest rate target?)