Saying they're a Ponzi Scheme over and over again doesn't make them one. Blaming the group for the individual is certainly in the zeitgeist, but it's still BS. There's so many ways it's not a Ponzi Scheme. Maybe Tether is? But Tether isn't all cryptocurrencies.
"... making unmediated online transactions securely in a trustless environment in this way is not without costs."
Yea, sure, but it doesn't support the thesis.
"Given that cryptocurrencies don’t produce anything of material value..."
How is that a given? What defines material value? Is the author a Gold cheerleader? Do they expect us to eat dollar bills?
"The 2008 financial crisis made clear why the financial sector must be brought under public control."
What does public control mean? They are, that's what the SEC is.