"A favorite argument of economic historians has been that the more plausible medieval objections to lending at interest are overcome by the presence of a competitive market for money that establishes a just common estimate of value. This implies that the only plausible objection is to the monopolistic exploitation of borrowers in the absence of credit institutions."
Joan Lockwood O'Donovan in "The
theological economics of medieval usury theory" (2001), in Oliver O'Donovan and Joan Lockwood O'Donovan, Bonds of imperfection:
Christian politics, past and present (Grand Rapids, MI: William B.
Eerdmans Publishing Company, 2004), 120 (97-120), italics mine.
A helpful (not to mention uncomfortable!) introduction to the "enviably balanced, penetrating, and, most of all, faithful theological comprehension of economic life" that is medieval usury theory (italics mine). Implied in this final paragraph, as supported by the body of the essay as a whole, is that that is not the only plausible objection.
Moreover, "the medieval vision of economic society runs [in so many ways] counter to the modern vision of a growth economy: of a system of ever-expanding production and consumption financed by credit."
For Lockwood O'Donovan, this is all recovered and forcefully re-stated by Luther, who, rejecting the distinction between the counsels and the commands, picks up again and re-stresses the evangelical commands in such a way as to buttress also the old arguments from natural law that had been somewhat undermined ("rewritt[en] . . . to accommodate free-market principles" (99; cf. 112-116)) by the Franciscans Olivi, Duns Scotus, and Odonis.
And Luther on the four degrees of "righteous dealing" (117-118, or the Long sermon on usury (1520), incorporated into the treatise on Trade and usury (1524; LW 45, 245-310) is challenging indeed.
Holy cow! "You were serious about that?"