Markets are voluntary, politics is coercive

Milton Friedman:

The political principle that underlies the market mechanism is unanimity. In an ideal free market resting on private property, no individual can coerce any other, all cooperation is voluntary, all parties to such cooperation benefit or they need not participate [...]

The political principle that underlies the political mechanism is conformity. The individual must serve a more general social interest — whether that be determined by a church or a dictator or a majority. The individual may have a vote and say in what is to be done, but if he is overruled, he must conform.

From ‘The social responsibility of business is to increase its profits’,
The New York Times Magazine, 13 September 1970.