What is wrong with Keynesian economics?

So what is wrong with Keynesian economics? Lots of things, but let’s focus on government expenditures. The Keynesian doctrine indicates that an increase in government expenditures is an “expansionary” fiscal policy. They talk and write about multipliers, pump priming, stimulus, and such. But it doesn’t work. Why?

So-called “expansionary” fiscal policy is a negative sum game. That is, the multiplier is not even zero, it’s negative. The Keynesian doctrine is based on ceteris paribus analysis (this just means that everything else is held constant). This is magic. If the government gives resources to Joe in the form of government expenditures, it must find a way to extract resources from Jim. Ordinarily, this happens by way of additional taxes or inflation. Unfortunately, it must extract more resources from Joe than it gives to Jim, because it must also pay Jerry, who works for the government and processes the transaction. The analysis should not be ceteris paribus. Instead, it should be mutatis mutandis (with all the necessary changes).