People have to be careful about what exactly was considered usury vs lending for investment. Distributists do not oppose investment if there is some actual risk involved and the investment is grounded on a tangible asset.

Not all loans were considered usurious. For instance, a business investment itself has some risk, and the person who made the law has a reasonable claim to the profits. But suppose the business is suddenly destroyed. The lender cannot claim a compounded interest after that point. At best, he is owed only the principal. Morgages are an example of loans that are not necessarily usurious. What we call the interest rates are something more like a rent-to-buy type thing, and if the house is, say, destroyed by some fire, even if you don't have insurance, the interest stops building up. Because the asset is gone, there is nothing now to ground your contract. At the worst, the remaining money is owed, but nothing more. Now, the interest rates might be excessive, and that's bad, but excessive interest rates aren't quite the same as usury itself.

A usurious loan is one that comes with no strings attached for the lender (in other words, no risk). The amount of interest is not what the issue is, but rather the nature of the stipulations tied to the loan. These are usually loans for consumption rather than for investment. Credit card, payday loans, and student loans are like this. The lender is given a guarantee by the borrower, but even if the money is used for some agreed upon thing (like, say, student loans), what is actually being negotiated is an I-owe-you by the borrower rather than some kind of return specifically related to the asset involved. Business loans are tied to the outcome of the business, but a student loan is incurred and interest compounds regardless of whether or not the student actually completes his degree and makes a good return on it. In some ways, these loans have an inbuilt arbitrage to them barring legal repercussions.