Usury is simple method of enslaving people in despair… It has nothing to do with profit or interest.
Also - many people do not understand clearly the compound percent - the fee is understandable for anyone.
A point on usury in the Bible- it is highly debated what it actually means and I wouldn’t side with the simple interest definition; it is more likely to be punitive interest rates. If you look at the the context where it is described pejoratively it is the context of exploiting the poor. ie you shouldn’t do it. Also other usages are in regards family of tribes of the nation of Israel and as such you cannot seperate usury from the purpose of the Mosaic law- to point to Christ as the one who would crush the serpents head prophesised in Genesis 3 and an attempt to bring the kingdom of God on earth through Israel. the latter point explains aspects of the Mosiac law which may not seem Rothbardian since the aim was keeping the land in israel’s and the specific tribes hands.
Now in the NT the locus of the kingdom of God is not a piece of land inhabited by the Israelites but in Church which may explain the complete absence of any teaching on usury in the NT. I would go as far to say that the NT endorses interest in the parable of the talents where one man is commended for putting money in a bank, essentially anyway, which earns interest and is called a good steward.
In conclusion it’s not as clear as you may think at first.
I do not say that there is any “cutoff point”, so I am far from opposing this practice in legal sense, or sending anyone to hell.
I do say that usury is a matter of human relations under particular circumstances - usually extremely hard for only one of the sides.
In my view (as above) usurers are nothing but brutish thugs robbering the weakest…
Part of Christianity’s problem with usury stems from Aristotelean scholasticism (especially that of St. Thomas). Aristotle deemed interest “unnatural” because money is “barren” (it doesn’t produce anything).