Why are liberals so ignorant of the failures of Keynesian economics?

the booms and bust are directly attributed to the mismanagement of the money supply. the thing is no one person or group of people knows what interest or the money supply should be that is the direct cause of the housing bubble internet bubble etc, etc, now we are seeing what Keynes meant by the long run we are all dead but it looks like the long run is here and we arent dead.