The law of supply and demand is a fundamental economic truth. One of its tenets is that when the demand for a value exceeds its supply, prices will rise. Conversely, when the supply of a value exceeds the demand, prices will fall.
The willingness of producers to manufacture a value for a particular price constitutes the supply. The willingness of consumers to pay a particular price for the value constitutes the demand. Both the supply and the demand are determined by the voluntary choices of individuals, as each seeks mutually beneficial trade.
In a free market, trade is voluntary. Each individual is free to produce the values of his choosing and trade them with willing buyers. And each individual is free to buy the values of his choosing from willing sellers. In a free market, an individual can mow lawns, write software, or build widgets and sell those products and services to those who are willing to pay for them. In a free market, if an individual desires a particular value, then he must earn it by producing other values to trade. If an individual wants to demand a value from the market, then he must supply commensurate values to the market.
Housing advocates want to restate the law of supply and demand. They are demanding that values be supplied to those who have not earned them. They are demanding that individuals be supplied with values even though they do not supply commensurate values to the market. And they want this demand be enacted into law. They want the law to demand a supply of values to everyone, regardless of their effort (or lack thereof) to earn those values. This is the meaning behind “housing is a right.”
Similar demands have been made for decades. As one example, rent control demands that landlords produce housing at a price that they do not choose. Invariably, the price set by rent control is below the price that would be established if the trade was voluntary. The results are predictable. The rental housing supply slowly decreases as landlords seek more profitable uses of the values they have created, such as converting apartments to condominiums. They seek voluntary, mutually beneficial trade.
When producers must give unearned values to others, they have no incentive to produce those values. When the law demands that producers trade values against their will, the supply will decrease. That, we might say, is the law of demanding supply.