Borrowing money you cannot pay back is the risky behavior.
Just because people were enticed by cryptocurrency doesn't mean that cryptocurrency is the problem. The problem is spending more money than you can afford to spend.
We already have a system of checks and balances for this. If you borrow more money than you can pay back, you take a hit on your credit that can last years, and banks will trust you less in the future for your high-risk behavior.
Anyone with a credit card should be able to use their line of credit to purchase anything they please - your history of paying the debt back is all that really should matter, not what you spent the money on.