Full recourse loans attempt to assert an ownership interest in persons, as opposed to (or in addition to) objects
Here is the Magisterium on the specific question (Pope Callistus III (1455-1458), Usury and Contract for Rent), describing a morally licit contract (full citation here):
But the [lender], on the other hand, even though the said goods, houses, lands, fields, possessions, and inheritances might by the passage of time be reduced to utter destruction and desolation, would not be empowered to recover even in respect of the price paid.
Even if the value of the collateral goes to zero, it was specified in the contract that that specific collateral is all the non recourse lender is entitled to recover
That is, a licit income-producing rental contract (which might or might not be labeled a ‘loan’ in modern language) is non recourse.
37) I see that the Magisterium and Aquinas have actually been clear that lack of explicit recourse to real assets is central to usury: that full-recourse lending for profit is what is defined as the moral problem. But why is that the case?
Usury involves treating people (subjects) as things (objects), because it involves purchasing “Bob owes me principal and interest” as opposed to purchasing shares in that project there or that bundle of assets there, distinct from particular persons. The most extreme form of treating persons as property is chattel slavery. (Some authors beg to differ, seeing usury as worse, and the argument has some merit). Usury is in the same moral genus as slavery.
Furthermore, “Bob owes me principal and interest” is not a thing which actually exists. Charging rent for literally nothing, no thing, is intrinsically unjust.
38) But you’ve said that intangible or only partly tangible things like patents and operating businesses can be ‘objects’, and thus can be property. So how do I tell the difference between what can be ontologically real property and what can’t?
Ontologically real property consists of objects. (Property in general refers to a relation between owners, subjects, and objects; but what we ordinarily call ‘property’ as a noun are the objects in this relation). Read more