If I find a funny-looking stone, and promise to give it to you in exchange for goods, it would be fraud to give the funny-looking stone to somebody else instead

If I find a funny-looking stone, and promise to give it to you in exchange for goods, it would be fraud to give the funny-looking stone to somebody else instead. Cryptocurrencies are no more "money" than the funny-looking stone, but one could still commit fraud with them.