There's an unusual aspect about these "crypto" things in that they are being touted both as replacements for traditional currencies (hence the term cryptocurrency) and as investment assets. That combination cannot work.
Regardless of any other properties, a workable currency must be stable, with the allowance of moderate inflation. A volatile currency only leads to chaos, historical examples of which are plentiful. Meanwhile, the only way to profit from currency-like instruments (tokens without intrinsic value used to represent actual value) is through fluctuations in exchange rates. The more volatile the currency, the greater the potential gains and, crucially, losses. In the long term, currencies of stable economies largely track one another, provided trade volumes are sufficient. If everybody adopted cryptocurrencies, that avenue to quick profits would instantly become a dead end.
Moreover, the limit, whether hard or practical, on the amount of "coins" along with the inevitability of people losing their wallets means that there will ultimately be a diminishing supply of currency (when paper money is lost, the central bank simply prints more). This leads to a deflationary economy, something any number of experts will agree is a Very Bad Thing. As much fun as it can be to deride economists, they are not all wrong all the time, as the cryptobros would have you believe.
This leaves the possibility of crypto-tulips as potential investment assets. Again, bad idea. The only "value" they represent is the expectation that someone will be willing to pay more for them at some future time, based on the very same expectation. That can't continue forever. Sooner or later, the supply of new buyers, or shall we say marks, will dry up, and the last to enter the game will be left in the hole, having financed the winnings of everybody who came before them. Simply put, it's a Ponzi scheme.
Regarding value, most of the hype around crypto-tokens these days centres around their valuation in terms of established currencies, usually USD. Any increase is trumpeted with vigour while downturns are dismissed as momentary setbacks. Social media is (or was, until a few weeks ago) full of people boasting about how much their holdings have increased in value. What this fails to recognise is that most of this "value" cannot be converted to real, spendable currency. The exchanges have nowhere near the requisite liquidity, should there be a surge in demand. In other words, actually accessing those gains relies on an influx of buyers. In other words, it's a Ponzi scheme.
Yet another problem with "crypto" is the absurd energy consumption. A single Bitcoin transaction consumes over 2,000 kWh of electricity [1] while Ethereum demands a little more than 200 kWh per transaction [2]. While the latter figure is obviously better, the amount of wasted energy is still ludicrous. At current electricity prices, an Ethereum transaction costs around £60. Imagine having that much added to the total every time you shop for groceries or have a pint at the pub. With the average value of a card transaction in the UK being around £50 [3], this is comparable to having a VAT rate of around 120%. Obviously, someone has to pay this extra cost. Who is this, and where does that money come from? The money comes from people "investing" real currency in crypto. Without continuous new investments, the system would collapse. If that sounds familiar, it is because such an arrangement is commonly known as a Ponzi scheme.
No matter how things are twisted, the inescapable fact remains that every gain in "crypto" today is a loss taken from someone down the line, someone who will get nothing in return. That, to me, makes the entire endeavour unethical.
1.
https://digiconomist.net/bitcoin-energy-consumption/
2.
https://digiconomist.net/ethereum-energy-consumption/
3.
https://www.finder.com/uk/credit-card-statistics