For cryptocurrencies, there is no physical basis in value such as specie, nor the backing of a national bank (“fiat money”). Instead, cryptocurrencies value—such as it is—is in being a verifiable medium of exchange that is also technically anonymous. It does this by encoding every successive transaction in the blockchain through the use of a cryptographic hash, which is just a one-way encoding algorithm. (The details of the hash algorithm aren’t really important; just realize that as more exchanges happen, they are ‘mined’ (i.e. hashed)). The mining activity actually comes with a fee (a coinbase) which increases the total amount of bitcoin. Because of this hashing, Bitcoin and other cryptocurrencies are virtually impossible to counterfeit; it is like making exchanges under the auspices of a regulated bank but without having to deal with the bank.
Why is this valued? It allows you to make exchanges outside of normal currency regulations. You can ‘transfer’ funds internationally, or pay for things without paying a sales tax, et cetera, and because it isn’t regarded as an actual currency exchange governments don’t really have specific laws regarding ‘crypto’ until it is converted into actual money. You can also conduct various illegal or extralegal exchanges with it, or blackmail someone into emailing you Bitcoin in exchange for unlocking their computer that you jailed with malware. But for the most part, it is valued like a commodity, i.e. something to speculate upon regardless of its intrinsic value.
However, although you can ‘own’ the wallet containing the cryptocurrency anonymously, when you go to exchange it with some kind of actual currency you are going to have to reveal your identity to someone, be it a bank, and exchange, et cetera, so as a scheme for laundering drug money or bankrupting an evil corporation it doesn’t make much more sense than Hans Gruber steeling $600M in German bearer bonds; regardless of where you transfer the cryptocurrency, when you try to cash it in someone is going to ask where you got all of this money. Unless you are able to buy real estate, luxuries, or groceries with cryptocurrency you are still going to have to turn it back into dollars or euros or Kruggerands or whatever. And while people often seem to think that Bitcoin and other cryptocurrencies are “untraceable”, the truth is quite the opposite; while the wallet owner may be anonymous, the transactions are not, and it is quite possible for a forensic accountant to back out where the ‘money’ has been and to a large extent who has been touching it. There are cryptocurrencies that are actually more anonymous than Bitcoin and which obfuscate exchanges, but that degrades the ability to verify the authenticity of the currency via a blockchain.
Are Bitcoin and other cryptocurrencies ‘Ponzi schemes’? Not in and of themselves; as a medium of exchange they are just as ‘valid’ as national fiat currencies, i.e. they are worth what people are willing to exchange for them based upon a general consensus or fiscal index. However, because of all of the market speculation they tend to become even more inflated than national currencies, and there is no way for any government to really control or regulate them other than to pass laws making it illegal to exchange them for their own national currency. However, I wouldn’t go putting all of your investments in ‘crypto’ because there is absolutely no guarantee that the entire world won’t wake up tomorrow and decide that your “KittyKoin” crypto that you just invested your life savings in is just a big joke by an odious billionaire playing a giant practical joke and now all you have is a hard drive with a bunch of meaningless random codes on it.
Cryptocurrencies also have numerous downsides. With physical currency, there is the cost of printing or minting, and digital fiat currency of just maintaining traceability of transactions; while these are not inconsequential costs, they are relatively small in the scheme of the overall value they represent. For cryptocurrencies, however, the longer they are in circulation the more complex the hashes become and therefore result in geometric growth of the energy to process them. They also require high performance computing hardware; if you are wondering why graphics cards have become so precious in the last decade, this is a primary reason because the GPUs in these cards are ideal for ‘mining’ cryptocurrencies. Eventually these schemes will all become non-viable as the energy requirements to maintain them take more value than the coins themselves represent.
As for non-fungible tokens (NFTs)…I have no explanation. They’re “digital assets” that not only have zero physical manifestation but often don’t even represent anything of ostensible value. It is like someone played “Second Life” and said to themselves, “What if we could take the digital things we make here and sell them in the real world?” As far as I am concerned NFTs are completely a Ponzi scheme. But then, people spend thousands of dollars on shoes that they’ll never wear for fear of creasing the leather, so I’m guessing that we’re rapidly approaching the Shoe Event Horizon anyway. At least NFTs don’t take up any space or produce physical residues.