Any alternative currency used on even a relatively minor scale represents a dire & imminent threat to every power of fractional reserve banking entities. With each incremental increase in the widespread acceptance & use of currencies other than that which these fractional reserve banks create (directly or indirectly), the rate of freefall of collapse of their fiat monopoly accelerates exponentionally.
Once people can spot the fundamental illusion that is the foundation used by Modern Money Mechanics (that the "money" they are told exists in the form of fiat has illusory value), they are then able to connect the dots and spot the deception that's present in the rest of the system, which is an elaborate hoax, in reality.
Monopoly fiat, backed by the force of law that sovereign states posses, is the only way to perpetuate economic systems whereby the real rate of productivity can be in decline, yet the decline, which will translate into a lower standard of living for the overwhelming majority of the population, can be delayed long enough so as to allow the kleptocracy class to concentrate their ownership of assets that represent real wealth. It's "simmer, not boil, the frogs," in [political & economic terms.
There's no real 'debt' from the perspective of a fractional reserve central bank; it's hard for those steeped in conventional economics to rip out the notion from their brain that the fractional reserve central bank can't lose anything (they didn't lend anything of value or that cost them anything - they have ZERO skin in the game), and that their favored entities that are TBTF have only slightly less risk (because they will always be able to socialize their losses via taxpayer bailouts in the wake of busts, while they retain their ill-gotten gains during the booms), and that what most refer to as debt in this system is only a liability for the debtor. If the debtor doesn't repay what was they borrowed (a monopoly currency that cost the lender nothing to produce), they can lose their farm, construction equipment, home, machinery, infrastructure, vehicle, etc. that was used to securitize or collateralize the loan, or even if the loan was unsecuritized, they can at least see their revenue or wages garnished, be sent into involuntary bankruptcy (where their general pool of assets will be seized upon by creditors, including lenders), and squeezed in other ways.
The only way to avoid this is to not play the game. During crack up booms, you miss out on fiat-based gains, if you don't play the game, and the incentive for playing that game is that if your timing is correct, you can get rid of all debt and convert the excess fiat gains into hard assets having inherent value or other things of inherent value, before the fractional reserve alchemists induce another inflationary-deflationary (or vice-versa) harvest.
If one were fortuitous enough to play the game, and have the skill and/or luck to convert fiat gains into real wealth before the boom turns to bust, they'd probably be idiotic to repledge their real wealth assets as collateral for loans ever again (I say probably, because there are exceptions to every general rule, but these people would have to be either extremely lucky in their timing in terms of cashing their "chips" of fiat in for real wealth, or connected to the alchemists in such a way that they'd be assured a bailout in the event of another bust whereby their real assets are pledged as collateral for fiat loans).
The Harvest is the end game for the fractional reserve bankers and their minions. As just one example of the rape that is harvest, even generations of families that were land rich (let's say a family that has owned two square miles of prime farmland yielding high value crops for three generations, carrying no debt) can find that an economic downturn suddenly forces them to take the step of obtaining a loan, pledging their farm and equipment as collateral, in the belief that the loan will allow them to survive the downturn and become more profitable at some future point - they're now 'harvestable.'
Alternate currencies, readily accessible and readily accepted, are the kryptonite of fractional reserve banking & Modern Money Mechanics.