the default case is what's easiest to talk about with the traditional toolkit, not what's normal.
the default market in the marginalist economics tradition is the competitive auction market, so a competitive auction market can be assumed by default in a discussion without requiring a defense, but any other market requires defense.
However, this explains why economists attempt to convince politicians to turn everything into competitive auction markets. Energy liberalisation, emissions trading, anyone? When the capital development of a country becomes a by-product of the activities of a casino, the job is likely to be ill-done. — John M. Keynes
