It's not a double-standard. Complaining about a wrong action (like speculating on food¹) is not the same as complaining about a system that makes a wrong action possible (like cryptocurrencies). Much like one can defend the protection of speech one despises.

The equivalent would be to complain about specific uses of cryptocurrencies, or in the other direction, about the very existence of banks and commodity markets.

¹ (just taking your example, not necessarily my opinion)