Blockchain has specific address allocation and wallet address are transparent so it's still traceable. The area of concern bitcoin want to address is centralization of transactions that's the reason they decentralize but as time goes and by rising of many miners with powerful servers and lack of governance it is going back to centralization. Another is security it's not hack proof but it will take a lot of computing power to hack a specific wallet address provided that the user is not so careless. With regards to being used in crimes well FIAT is still the major currency used in crimes up to now. I think cryptocurrency has a big part in the future of managing almost every transactions.