The moral and religious condemnation of charging interest on a loan — originally a ban on any interest at all, later narrowed to mean only excessive interest. The prohibition runs through Aristotle's argument that money cannot breed, the Hebrew Bible's rule against lending at interest to fellow Israelites, the medieval Church's councils, and the Islamic ban on riba, before loosening in the Reformation and surviving today as interest-rate caps and the politics of payday lending.
Usury is one of the oldest arguments about whether it is right for money to make money. For most of recorded history the answer was no. To lend a sum and demand more back was treated as a sin, a crime, or both, condemned by Greek philosophers, banned in the Hebrew Bible, hunted by medieval churchmen, and forbidden in Islamic law down to the present. Then, slowly, the line moved. What had been a ban on all interest became a complaint about excessive interest. The lender who once faced damnation became a banker, and then a respectable one. Yet the old judgment never fully died. It survives wherever a society sets a cap on how much a loan may cost and calls anything above it predatory. Many civilizations have drawn this line somewhere. None has stopped moving it.