Usury used to be illegal. It used to be hated by the true Church. It should still be. If usury is hated, should that hatred reserved for only the lender? If usury is sinful, is borrowing sinful?
When asked if usury is a sin, Thomas tell us:
I answer that, To take usury for money lent is unjust in itself, because this is to sell what does not exist, and this evidently leads to inequality which is contrary to justice. In order to make this evident, we must observe that there are certain things the use of which consists in their consumption: thus we consume wine when we use it for drink and we consume wheat when we use it for food. Wherefore in such like things the use of the thing must not be reckoned apart from the thing itself, and whoever is granted the use of the thing, is granted the thing itself and for this reason, to lend things of this kin is to transfer the ownership. Accordingly if a man wanted to sell wine separately from the use of the wine, he would be selling the same thing twice, or he would be selling what does not exist, wherefore he would evidently commit a sin of injustice. On like manner he commits an injustice who lends wine or wheat, and asks for double payment, viz. one, the return of the thing in equal measure, the other, the price of the use, which is called usury.
On the other hand, there are things the use of which does not consist in their consumption: thus to use a house is to dwell in it, not to destroy it. Wherefore in such things both may be granted: for instance, one man may hand over to another the ownership of his house while reserving to himself the use of it for a time, or vice versa, he may grant the use of the house, while retaining the ownership. For this reason a man may lawfully make a charge for the use of his house, and, besides this, revendicate the house from the person to whom he has granted its use, as happens in renting and letting a house.
Now money, according to the Philosopher (Ethic. v, 5; Polit. i, 3) was invented chiefly for the purpose of exchange: and consequently the proper and principal use of money is its consumption or alienation whereby it is sunk in exchange. Hence it is by its very nature unlawful to take payment for the use of money lent, which payment is known as usury: and just as a man is bound to restore other ill-gotten goods, so is he bound to restore the money which he has taken in usury.
Stupid people will tell us about risk premia that must be collected, the time value of money, etc. and how this justifies usury.
STUPID PEOPLE, TAKE NOTE. You are ignoring the metaphysical nature of PROPER money, which Thomas refers to in the last paragraph in the quote above. Read this again carefully and realize that the nature of money, like that of wine, makes lending at interest unjust. Citing your risks in the form of losses and opportunity costs is more evidence for the case against lending at interest.
If usury is unjust and therefore hateful, should that hatred reserved for only the lender? If usury is sinful, is borrowing sinful?
It is by no means lawful to induce a man to sin, yet it is lawful to make use of another’s sin for a good end, since even God uses all sin for some good, since He draws some good from every evil as stated in the Enchiridion (xi). Hence when Publicola asked whether it were lawful to make use of an oath taken by a man swearing by false gods (which is a manifest sin, for he gives Divine honor to them) Augustine (Ep. xlvii) answered that he who uses, not for a bad but for a good purpose, the oath of a man that swears by false gods, is a party, not to his sin of swearing by demons, but to his good compact whereby he kept his word. If however he were to induce him to swear by false gods, he would sin.
Accordingly we must also answer to the question in point that it is by no means lawful to induce a man to lend under a condition of usury: yet it is lawful to borrow for usury from a man who is ready to do so and is a usurer by profession; provided the borrower have a good end in view, such as the relief of his own or another’s need.
Read that last paragraph carefully. Thomas would only allow us to borrow to relieve need. Not want. Need.
Most borrowing being done to meet want is in fact hateful, borrower and lender alike being worthy of scorn.