Greetings, fellow Thomist. You are correct that usury is any amount of interest, and attempts to pretend otherwise are sophistical, but I suggest you may want to look again at corporate bonds and other non-recourse loans -- that is, loan where collateral is limited to specified asset(s). Look at Zippy Catholic's writing on the subject -- he was a finance dude, and a very rich self-made man. A non-recourse loan is more like taking an ownership share in something, and then renting it back. It's unfortunate that we use the same words (loan, interest, debt) for both full-recourse and non-recourse contracts, because they're entirely different things.

I agree that charging interest on a full-recourse loan is a wicked and disgusting thing to do to one's fellow man, and I'd say it's in the same genus as slavery. Usury is to fraud what robbery is to larceny. It's also interesting that the markets where usury is most prevalent (housing, college fees) are the ones that have seen the most insane price increases.