Critics of free market economics range from those who reject markets entirely in favour of a planned economy as advocated by various Marxists to those who wish to see market failures regulated to various degrees or supplemented by government interventions. Keynesians support market roles for government such as using fiscal policy for economic stimulus when actions in the private sector lead to sub-optimal economic outcomes of depressions or recessions. Business cycle is used by Keynesians to explain liquidity traps, by which underconsumption occurs, to argue for government intervention with fiscal policy. David McNally of the University of Houston argues in the Marxist tradition that the logic of the market inherently produces inequitable outcomes and leads to unequal exchanges, arguing that Adam Smith's moral intent and moral philosophy espousing equal exchange was undermined by the practice of the free market he championed. According to McNally, the development of the market economy involved coercion, exploitation and violence that Smith's moral philosophy could not countenance. McNally also criticizes market socialists for believing in the possibility of fair markets based on equal exchanges to be achieved by purging parasitical elements from the market economy such as private ownership of the means of production, arguing that market socialism is an oxymoron when socialism is defined as an end to wage labour.