You have it backwards.

Transparency makes it hard for big criminals to move money unnoticed.

Private servers and ledgers make it way easier.

Look at the Epstein case. Convicted sex offender and child trafficker who used JPM Chase for all financials related to the activity, including involving some of the bankers and their clients - and they were able to settle with the Epstein victims for millions. A few others died randomly right after.

That is totally sealed. Unable to be seen by the likes of you and me. Crypto currency would absolutely solve that. It would open up all the transactions and people would figure it out, and dox the pedos.

You could solve all sorts of crime with transparent banking even if it was by and large anonymous.