There is a fundamental contradiction within modern progressivism* between its economic beliefs and underlying philosophical beliefs.
North American liberals hold to Keynesian economic theory; all the standard-bearing liberal economists, such as Krugman, Ygglesias, and Stiglitz, are Keynesian.
Keynesianism is demand-side economics, where economic health is determined by aggregate demand for goods and services. A main goal of Keynesian economics is to keep demand high, so more goods are produced, which leads to increased employment, full-employment being a primary aim of Keynesianism. The government is required to interfere in times of low demand (ie. recessions and depressions) by spending money (it doesn’t really matter on what) to raise demand. Too much savings is harmful to the economy as it prevents spending.
This opposed to demand-side economics, where economic health is determined by the supply of goods and services. It calls for low barriers to production, to lower prices so consumers can purchase goods at the lowest cost. The government is required to remove themselves from interference so individuals can best optimize savings and consumption for themselves.
Essentially, the main theoretical difference between the two is whether the economy is driven by creation (production and investment) or by consumption (demand and spending).
On the other hand, liberal political philosophy is strongly opposed to consumerism. It is also strongly environmental in nature and oppose what they refer to as over-consumption. They’ll complain of artifical demand created by mass media, rage against planned obsolescence, and have their Buy Nothing Days.
Now, if you are more intellectually acute than the average occupy protester, you may have noticed something from my descriptions of Keynesianism and progressivism: they contradict each other.
The economic theory that the economy is driven by consumption and that the government must work to keep demand high is essentially a call for over-consumption. A theory where economic health depends on demand for consumption while aiming for full employment, is a call for people to buy things they don’t need so they can work more so they can buy things they don’t need.
Keynesian economics is consumerism.
Liberal economics necessiatates and prizes everything liberals claim to hate about capitalism.
So why does liberal economic theory contradict liberal political values?
It’s simple: government control.
Earlier I told you the main theoretical difference between supply- and demand-side economics, but that’s just theory and nobody cares much about theory. Much more important to why (most) people choose which economic theory they prefer is the practical implications of the theory.
The main practical difference in application between the two theories is the level of government control of the economy.
Liberals like Keynesian economics, not because they believe in the theoretical underpinnings of Keynesianism, but because it allows more government control over the economy.
The capability of free-market capitalism to produce goods and services is so obvious to see, that no one with any pretensions to intellectual seriousness can completely discard capitalism. The superiority of free-market capitalism is so undeniable that (most of) the left has given up fighting capitalism as a whole.
But progressivists are unwilling to give up their desire for control, so instead they have adopted mixed economic theories which use free-market capitalism as a substructure, then put a government regulation superstructure over the substructure so the elites can still feign control over the economy.
That is why their economic belief in Keynesianism (which is ideological consumerism) can so blatantly contradict their supposed values of anti-consumerism and environmentalism.
Keynesianism is only a superficial belief, a mere ideological tool to justify liberals acquiring what they really value: the expansion of the state.
* I use liberalism, progressivism, and new left interchangeably as there has been no real difference between them in North America since the McGovernite takeover of the Democratic Party (and Trudeaumania in Canada).