It is only through the supply side that innovation can be spurred, Keynes was not so much wrong, as narrow minded in his views; yes, if labor controls the economy, the wealth of labor will increase. Without the markets & supply increasing however, there will be no re input of that wealth. Products & services must increase in order for earned wealth to be reinvested in the economy. Thus Keynes should be discarded, old theory, and incompete.
Yes thats pretty much it.
A lot of economic policy from Roosevelt and even before centered on demand side. The thought was the Depression was caused by insufficient demand so measures were dreamt up to increase demand, like minimum wage rates and the like. It was hoped that higher incomes would spur more spending.
In contrast Reagan's advisors championed looking at the supply side. They suggested that creating incentives through the tax code to change behavior to encourage greater productivity would
cause higher incomes and eventually
more demand.
In sum the Reaganauts were correct. Their policies worked. The Reagan tax cuts were not targeted temporary cuts but permanent cuts to income taxes and others. It encouraged peoplel to work more and earn more. By contrast the Obama program is back to demand side focus, with targeted tax cuts and incentives for buying homes, cars etc. Those policies are gross failures, as the recent research on cash for clunkers showed.