And how many people use Bitcoin for crimes?
Everyone will have their own motive to support the crimes that they are doing.
If there is not bitcoin or crypto, they will also say that another thing is supporting their crime and used for their crime.
So, we cannot determine it. many people also have been using fiat money for any criminal, money laundry, and other illegal activities.
This are one of the reasons crypto is still rejected .
as far as I know, the reason Bitcoin is rejected in some countries is not only related to the use of criminals. But more other reasons like they are afraid of the financial system of their country, risks, and more about government cannot control Bitcoin. Additionally, sometimes, they don't legalize Bitcoin as a tool of payment because they have authorized the "money" in their country is the Fiat itself, not a cryptocurrency.
And I also agree with @Upgrade00. Fiat is used for numerous criminals for a long long time ago. But none rejects it so far.