Not true by any means. Fiat is the tried and true way to commit crime. Having transcations on a ledger forever, works against your criminal take. You are just repeating.
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
Criminals don't really need strong anonymity as long as the payment system has strong censorship resistance and at least one counterparty won't mind accepting "tainted" funds.
Arguably, privacy is much more important to non-criminal individual users as they themselves can be targeted by criminals as a result of their income/holdings being globally visible, and unlike organized crime, they often have less means to protect themselves from $5 wrench attacks.
[1] Source: I watched many crime thrillers growing up
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.
Crypto is entirely dispensable. It is pseudonymous, by design resists regulation, and has no enforcement. Some chains are deliberately opaque (Monero, Zcash), and there are tumblers to obscure flows even further. Its approach to money laundering is "sure, bring it on".
Fiat is indispensable, and better for legitimate purposes than crime. Crypto is dispensable, and better for crime than legitimate purposes. We should dispense with it.