The Neoclassical Synthesis was taken as an article of faith. Fundamental questions about the failures of the market system, such as the causes of periodic depressions and the unemployment that accompanied them, were avoided.
That was building up during the '50s, in the so-called neoclassical synthesis, better called the neoclassical-neo-Keynesian synthesis, I think. The main thing was that classical economics didn't explain the Great Depesssion and didn't give you any hope of solving it. Keynesian economics did.