* Giving criminals and scammers the ability to exchange goods and services anonymously.
* Providing a source of funding North Korea's nuclear weapons program
* Allowing nation states to engage in global commerce despite sanctions because they won't stop killing innocent people
* Convincing older and gullible people to give their money to someone they don't know and a technology they can't explain
* It's the future!!
EDIT: Couple more
* Transactions are so energy intensive that the currency eclipses the carbon footprint of many countries
* Those transactions are also incredibly slow!
* Matt Damon!
I think there is a use for blockchain, but as a technology for everything from buying groceries to countries using it as a currency, no.