According to literature cryptocurrencies can help avoid double spending and generating of fake currencies into the system. The blockchain technology which serves as a distributed ledger system for all transactions of bitcoin prevents double spending and also because the honest nodes on the bitcoin network outweighs the attacker nodes, the nodes within the network only confirms true transactions unto the blockchain other than any suspicious transactions.
Also, because the blockchain technology is an open source decentralized network everything occurring on the network is very transparent and therefore people can just make their own currencies into the system.