Moral persuasion and reasoned discourse would always remain most invaluable in the battle against moral degeneracy. One (in this case the father of the 12 year old) must logically show that particular actions and modes of being would be very costly if continued.
Market-determined interest rates—whether high or low—rather than artificially induced ones via credit expansion or contraction, help allocate capital to those lines of production which aim toward the satisfaction of most urgent wants. “Usury” would be a mere value judgment, not a valid concept under a free market regime. Sound economics must be propa. Cheers!