> Having transcations on a ledger forever

Do you think cash transactions don't have even more detailed ledgers? The "tried and true fiat" has been used to catch criminals for centuries because banks keep very detailed records of withdraws and deposits.

> You are just repeating

You are just repeating. Obviously both are being used for crime

> Not true by any means. Fiat is the tried and true way to commit crime.

Depends on the crimes, and up to certain values/volumes.

For 'consensual' transactional things for goods/services it could be useful (e.g., drug deals). But for ransom-like stuff, where one end of the 'transaction' is not thrilled with the 'deal', having to physically pick up the cash puts the perp at risk.