NOTE: data in this article is recent as of 1/4/2022.
The vast majority of cryptocurrencies are ponzi schemes.
Nobody actually uses them as currencies to buy stuff (except criminals to avoid being caught), and everybody using them as a way to make money.
Because the only way to make money is by selling to the next investor (zero sum game), and
there's no other legitimate and pratical use for the vast majority of owners, this is a ponzi scheme.
Basically it's a gamble that you'll bail before the bubble bursts or lose a lot of money.
The only exception I know of is Monero, and as I explain why cryptocurrencies are a failure as actual currencies
I'll describe what Monero does to fix these problems.
Monero isn't perfect but it's viable and the best option available to my knowledge.
Why create a new cryptocurrency in the first place?
Online money transactions, replacing Paypal, Stripe, credit cards, and such.
Paypal's fee is ~3%, and online transactions are in the trillions of dollars so it's significant.
To be a viable replacement the fee needs to be lower than Paypal's (ideally 0), and transaction time low enough to be practical.
Paypal's fee is 2.90% + $0.3 (in most cases, Paypal got a complex fee system).
bitcoin's average fee is ~$2.78, which is higher than paypal in most cases (break even point is ~$85.5), and transactions are slow.
Monero's average fee is ~$0.026 and few minutes transaction time, and
it's designed to keep the transaction fee low.
Governments don't control the supply of crytocurrencies, so it can help protect
people from decisions that lead to high inflation, which can be seen as a hidden tax.
Lower taxes = good for the people.
You don't need a bank to store your cryptocurrency, which means no extra fees to pay.
Bitcoin got finite supply, leading to deflation instead of neutral or inflation means spending is a bad choice, thus not viable as currency.
In addition as wallets get lost you lose pieces to trade with.
When people die it's very likely that their wallets will be lost, and in few generations there won't be enough pieces to trade with
for smaller transactions.
Monero doesn't have finite supply, so its value its more stable and it's sustainable.
Bitcoin's control is getting centralized to those who live in places which cheap electricity and who buy specialized ASIC hardware
since they're the only ones that can be profitable.
Monero uses a hash function that's inefficient to mine on
ASIC by using dynamic computation so you can't hardcode it to the wires,
and GPUs by using lots of memory so having many cores doesn't help since there's not enough memory for each one.
so Monero is only viable to mine on CPUs, which everyone have thus everyone can mine profitably,
keeping control more decentralized.
Another problem is that as the blockchain grows it takes a lot of storage space, making it impractical for home computers to host it.
Currently Bitcoin's blockchain's size is 461 GB.
That means that eventually people will have to rely on remote nodes to make transactions.
While Monero's blockhain's size is smaller, as far as I know it doesn't have a solution for this problem.
There are bad people in the world who seek to cause harm to others.
political, religious, superiority complex, tribialism, greed are some of the reasons they do this.
Donated to a political party they hate?
Sexual orientation they don't approve?
Or maybe just straight foward criminals that are looking for victims.
Being able to see your transaction history can lead to unjust harm.
Monero is private, transactions can't be traced back to wallets.