Who are you defrauding? Under what jurisdiction? The ability to be 51% attacked is a feature of the design. You expect all the actors to commit enough computing capacity to prevent such an attack as it’s in their own best interest.
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.