That is entirely not true. Crypto currencies are not a fraud in general. scam exists in everyday life. spotting scam in the virtual world is easier and faster. hacking and stealing crypto currency is a different issue altogether.Cryptocurrencies that are not backed up by governments are a scam. The only reason some people make money out of them it is because of the greater fool theory. However unlike real estate or Art where the greater fool gets something out of his payment. Cryptocurrencies are empty and devoid of any comfort or emotional value which makes them even more vulnerable and have less greater fools. You might end up being the greatest fool yourself.
Crypto currency cannot and will not replace real world currencies because the relation between them is mutual.
crypto currency is not without back-up. If you watch a lot of youtube videos from channels of extreme crypto miners .. you will conclude that as long as silicon valley and china's manufacturing empire exists and energy is available. crypto currency will survive. when you are buying computers and graphic cards and upgrading them continiously to stay in the game .. you are spending real money and good deal of real money. not to forget electricity bills.
what more currency back-up do you need? for example bitcoin: as the encrypted formula becomes more complex and big. it needs more processing power to decrypt it. it is a never ending circle. a life by itself.