Gambling. Crypto is globalized gambling. It's a money laundering vector, for sure, but for the same reasons crypto competes poorly in the transaction market it's close to a last resort for high-volume launderers.
Completely and utterly unlike and in no way whatsoever similar, at all, to stock markets, futures exchanges, CFDs, options, CDOs, etc, etc, etc.
Crypto is just a speculative digital asset. Sure it's been a playground for all kinds of scams and charlatanry, because there's no oversight, just as stock markets once were (and still can be in some areas eg pink sheets), but crypto is not a scam in itself.
Those things are backed by cash flows, which crypto isn't because noone ever wants their coin to be considered a security.