Actually in a libertarian world this would be much less likely to happen. Libertarians are more in favor of gold standard, and most are very against fiat money. One of the main things the banks do is fractional reserve banking, where they can loan out more money than they actually have. This is only made possible because of the government, and the only reason fiat currency has any value at all is because the government demands that taxes are paid in it. Libertarians are generally against the idea of taxation, which means they generally view fiat currency as being inherently worthless. In a libertarian society, a bank that loaned out more gold than it has would be considered to be engaging in fraud, and all of the fiat currencies in the world would be seen as about as valuable as toilet paper. Your biggest mistake is in thinking that these banks etc are operating in a free market, they certainly are not. In a free market Bitcoin would be able to compete with the Dollar much more so than it is now, there would not be regulations on money exchangers etc (ie: no know your customer), etc. So really you are not playing devils advocate against libertarians, because the only reason that these things are happening is because of the government and the lack of a free market.