Bitcoiners are going to have to learn this soon.
Many people believe that usury means charging excessive interest rates. But, it is not. It is charging ANY interest.
It is a mathematical problem.
Such as, if you put 1 ounce of gold in a bank at 4% interest back when Jesus was walking around, today you would have more gold than all the gold in the world.
It is the problem with our currency today, they create the loan out of thin air, but they do not create any currency to pay the interest. And there has never been enough currency to pay back all of the loans. And today, there is probably not enough money to pay off the national debt & interest. And, if there was, we would pay that off, and there would be no currency left.
And this is with an expanding money supply. (well, that is the only reason it has gone on so long)
With bitcoin, it will be a very short while before the interest owed is more than 21 million bitcoin.
Compound Interest Cannot Exist In Nature
The thing closest to a power curve in nature is microorganisms that constantly divide to create more of themselves, as long as there is food available. So, they double and double and double, and then they all die.
Larger multi-celled organisms run into the limits of expansion much quicker. And most have a method of balancing themselves out.
Even low percentage power curves quickly eat up the entire world.
Many "retirement planners" like to say that the stock market grows 10% per year (or 7%, depending on bull or bear) but has it really?
Is CocaCola really 10% bigger than it was last year? Do they sell 10% more Coke products? Did they hire 10% more people? If they haven't, than that 10% increase in stock price is only paper gains. And that is only because of money printing.
If CocaCola can actually increase 10% per year, then how can Pepsi still exist? All of the people, all over the world, should now be drinking Coke. And without the planet's population expanding, there would be no more growth available. Again, the growth is fake. The price of the stock has only gone up because there is more paper in the system.
Money printing (without creating goods that people want) is a sin
Fractional Reserve lent, debt based, fiat currency is extremely damaging to the society that lets it exist. If you print currency without creating goods (that people want!) than you are causing inflation. This is a hidden cost on all people who use the currency.
Such as the stock market going up 10%, that is paid by all the people losing 10% (or more) of their purchasing power. And what is worse, is that those who aren't investing in the stock market also pay. Those in the stock market barely broke even. Those who put their money in a savings account at 3%, lost 7%. And those who aren't investing in the riskiest of assets lost everything.
They say that compound interest is a very powerful force. However a compounded loss is even more destructive. At a 10% real inflation rate, people lose half of their wealth every 7 years. If a person works 50 years (49 = 7 x 7) their original dollars they made is not even worth a penny. Nearly everything they made in their youth is as if they never earned anything.
You know, people bought a house back then for $17,0000, which today is valued at $1,000,000. If they instead saved that $17,000, they couldn't even afford rent for a year today.
This is, supposedly the stuff that bitcoin saves us from, but only if we get rid of all interest.
Why we cannot charge interest on bitcoin loans
The problem is easier to see if we include the entire pie (economy).
If we just look at a single person, and they want to borrow 10 bitcoin, and are pretty sure they can start a company and make 11 bitcoin to repay the loan and interest, well then you might think that is all ok.
But, if we look at all the people borrowing, we run into a problem where soon, the interest owed is more than 21 million bitcoin. The principal may or may not have been paid, but the interest keeps growing.
And, if you play this game long enough, one person ends up with ALL the bitcoin. (or, are at least owed all the bitcoin) (This is the game the banksters are playing right now. In the end, the house always wins, and so do the banksters, if allowed to exist)
An easier way to visualize this is a knight offers this town some coins, so that they can more easily buy things (instead of just barter). He gives the butcher, baker and candlestick maker 10 coins, and says if they do not pay him back 11 coins in a year, he gets to take all their property.
You should be able to make one more coin, right?
Well, you cannot. There are only 30 coins in existence. There is no way that 33 coins exist after a year, no matter how much they sell. If we stop the economy and take a picture, we will find pictures like 9-9-12, 10-10-10, 9-10-11, 8-11-11 and really it just depends on what time of year the knight comes back who will lose their property.
There is no way to pay for the interest.
And it is the same with bitcoin.
Sure, one person could make more bitcoin and pay back the principal and interest. But, all the people, totalled cannot. When you add interest to a financial system, then you are making it so that the slowest person goes bankrupt. Not because of anything they did, but because there is never enough money in the system
This is why usury means ANY interest, and why usury is so bad.
It is also the reason why the Bible says to forgive loans every seven years.
Now, why would you lend your bitcoin out for 0%? Well, if you lend the bitcoin to build a house, and the builder pays you back, then you have all your bitcoin still, AND the world has another house. The world is richer. Your portion of it, expressed through bitcoin (money) is now worth more.