The Church teaches as the viceroy of Christ the King what moral principles need to form economic laws and transactions.
Liberal Economic Philosophy says any choice which increases net wealth is a good choice; the principle acknowledges no limit.
If application of usury teaching was difficult in the sixteenth and eighteenth centuries, it is certainly more so today.
Usury is the sin of charging a profit or gain for the loan of something which is consumed in use such as money.
Just price theory is not solely a matter of divine law; it is part of the natural law as evidenced by the fact that even pagan Roman law recognized it.
Liberal Catholics who hold Capitalism to be an article of the faith love property, believing that it proves that the Church supports the Capitalist ethic.
How much should the government exercise its monopoly over interference with economic activity? Capitalists say not at all and Communists say all the time.