Perhaps this is ignorance on my part, but my limited understanding of bitcoin suggests that new bitcoins cannot be created by creating a loan. It would be impossible to use a fractional reserve system with bitcoins by definition. This distinction is important since over 90% of US currency is created via loan using this fractional reserve mechanism.
Unless people decide that bitcoins are not fungible, then fractional reserve banking is absolutely possible with them. You give me Bitcoin, and I will lend them out at interest, keeping some on hand to give back to you as you need them. The process is identical to banking with a fiat currency, and results in the same money multiplier.
Where there is confusion is because economists accept that money is an abstract thing, backed by people's willingness to accept it, whereas Bitcoin enthusiasts see money as a tangible thing that must be backed by a concrete thing. Thus, when economists say that the supply of money changes with fractional reserve banking, they are referring to dollars in the abstract, not physical dollar bills. When Bitcoin enthusiasts say that the supply is limited, they are referring to the bitcoins themselves, not the abstract availability of bitcoins.
> This distinction is important since over 90% of US currency is created via loan using this fractional reserve mechanism.
No actual US currency is created this way, we just have a strong social convention of treating “the bank owes me $1 on demand” as equivalent to “I have $1”.
So if I make a “deposit” (which is, on point of fact, a loan) of $1, and the bank retains $0.10 in reserve and loans out $0.90 to someone else, we say that I have the equivalent of $1 and the borrower has $0.90, so it seems that $0.90 has been created. But there is really only $1.00 of currency, of which the bank has $0.10 and the borrower has $0.90. I don't have a currency, I have a right to demand (with certain conditions, depending on the kind of deposit) currency from the bank.
Most dollar-denominated trade is actually trade in future claims of dollars rather than actual dollars. Nothing [0] stops a parallel thing from happening with Bitcoin; obviously, such trade would be distinct from exchanges of Bitcoin recorded in the Bitcoin blockchain, just as trade in future claims of dollars are readily distinguishable from exchanges of physical greenbacks.
[0] Except the current immaturity of the Bitcoin ecosystem compared to the banking systems of any developed economy, but that's presumably something that would change were Bitcoin to achieve broad, durable acceptance.
