Crypto has no use that generally benefits society. It's great for the inventors and early investors of a crypto that happens to get popular and take off. These people can get rich, but they are not creating anything. It's the best thing since sliced bread for black marketeers, who need an easy and relatively untraceable way to transfer money. From drugs to human trafficking, crypto is the currency of choice. It has transformed ransomware from a niche criminal activity into a true big business for organized crime. And it's an opportunity for speculators to gamble and get rich or get wiped out, depending on their luck or skill timing the market. And the costs to society are immense, from the wasted fossil fuels and resulting carbonization of the atmosphere, to the crime that crypto facilitates.
For normal financial transactions it is terrible: You cannot dispute a fraudulent transaction, and the value is horribly unstable. Every purchase or sale becomes a speculation: Will a coin be worth double when I spend it compared to when I got it, or will it be worth half? The only near certainty is that it will not be worth the same unless I spend it the instant I receive it.
It's a scam from start to finish. It probably cannot be stopped, because of the nature of the internet, but the people running the scam are accessories to the crime which is its only real use.
That would be a legitimate use of blockchain (if it works, which I'll take your word for.) Has no bearing on the Ponzi scheme which is cryptocurrency.
I will respectfully disagree with most of that.
1. Benefit: Direct control of your money and how it gets held and transferred. No 3rd parties involved, no counterparty risk.
2. Criminal activity: Criminals have used many "untraceable" stores of value, including cash, gold, and diamonds. There's nothing inherently criminal about any of those, and crypto is no exception. Where there are criminals, they will attempt to move their stolen goods by any means.
3. Energy use: See above for the proof-of-work/proof-of-stake discussion regarding the energy usage. That will eventually go away.
4. Volatility: The only reason that cryptocurrency is volatile is because it is compared in price to other currencies which are viewed as "stable". But if you're not interested in turning your Bitcoin into dollars or euros or pounds, then that's irrelevant.
5. Fraud: Transactions in cryptocurrency are the same as cash -- you of course can dispute a fraudulent transaction, through the courts -- the same as you'd do if someone stole cash from you. You do not have the luxury of complaining to the payment provider like you do with a credit card -- but on the other hand you don't pay exorbitant transaction fees and account fees either.
6. The references to "Ponzi scheme" or "scam" are ridiculous. Ponzi schemes pay previous investors with the influx of money from new investors. That's not how cryptocurrency works, and the blockchain is 100% transparent and free for anyone to examine for proof. Your actual complaint, and what you mean to say, is that you don't trust cryptocurrency as a store of value because there is no one guaranteeing that value. Well, I have news for you. That's the same thing as gold or diamonds. All of these things are worth only what people are willing to pay for them.