Quote from Cutten:
There is no difference, at least not in the realm of government, law, politics etc - any applied school of knowledge, basically. Something must be judged on how it can be implemented in the real world. Communism is a good example. In theory, IF people are all "altruistic", communism might work really well. Since in the real world they are not "altruistic", communism is a total disaster when you try to implement it in reality. You cannot implement any system in theory, you have to implement it in the real world with all the constraints that entails. Thus all theories must be judged on their actual or prospective implementation.
If Keynesian economics works given certain theoretical conditions (which is extremely debatable), but those conditions are untenable in the real world, then it will be a failure no matter how sound its theoretical position. Same with free market economics. If voters will go socialist before a free market economics liquidation/recession can run its course, due to their economic ignorance and general fear, then even if you support free markets in theory, you have to recognise it is untenable since voters will reject it and lurch leftwards. Thus some intervention in serious recessions would be preferable, even for Milton Friedman or Murray Rothbard, because failure to intervene would result in socialism via the ballot box, whereas intervention would result only in somewhat watered-down capitalism.