I also think people are able to track and trace crimes so it's a way of getting a proper measurement. You can't really do that with fiat.
The basis is only the reported crimes, usually these are big crimes and I'm sure there's more that are not reported yet.
Crypto is easy to monitor compared to fiat as paper money is hard to monitor, once it's out in the bank, it can easily be launder.
As long as there is a regulation by the government, they will be in control and will be able to monitor the movement of crypto.
That is gonna be possible as people will be required to register and comply with the KYC, that way, they(government) will know who owns the address.
I wish all the governments were consisting of honest people so that they wouldn't abuse the regulations. Unfortunately, in many countries this is not the case. In reality, governments and criminals are often not two opposing parties, there are criminals in the governments.
If we want to decrease the number of crimes involving crypto by regulating it in a given country, we should also consider the number of crimes involving government in that particular country.
That two are different, every country has different government and therefore not all government are corrupt.
We can solve the corruption within the government if we will select a good leader, we should not sell our votes, I'm discussing this since its happening in some countries, in addition, plunder or any form of corruption which is destroying the public trust of the people should be punishable by death penalty.
That's gonna be a long discussion as everyone might have difference opinion as we cannot avoid our religious belief will also be considered here.
I will still stick with my opinion that regulation would reduce crimes in crypto since it's impossible to totally eradicate it.