So, I watched this video today. It explains how charging interest (usury) is immoral because it is mathematically impossible for every person to pay their loan back.
I got to thinking about it and it kind of makes sense. Here's my understanding of what the guy in the video was saying: See, our banking system is what is called a fractional reserve system. What this means is that banks can loan out more money than they actually have. In other words, when you borrow money from the bank, that money is created out of thin air--it is borrowed into existence. Al fiat currency is created this way. Say that one million people were loaned $100. So, $100,000,000 is created out of thin air. All of that money must be paid back plus interest. The problem is, there isn't enough money to pay back all the loans plus interest. Remember, that since all money is created this way, loans + interest is greater than the supply of money.
I think this argument is fine as far as fractional reserve banking is concerned, but most of us aren't bankers. Since there are a lot of people who don't pay off their loans, there is a lot of money out there that just circulates and acts as a medium of exchange. It's also used as a store of value (although a poor one). If I'm saving for retirement and you want to borrow some money from me, I'll be taking a risk if I decide to loan you any. That risk can be mitigated by charging interest. Since you are presumably working and creating value where it didn't exist before, I see nothing wrong with this arrangement.
Heres the video I was talking about: