Have they also ever thought that cash can also be used for small-scale illegal transactions in a smaller scope? Maybe they also have to live in a country with a high crime rate, where minors can also own weapons without a license, drug trafficking by gangsters school-age children using cash. There is no transaction information, everything escapes government monitoring.
That is, if traditional financial methods are not sufficient solutions to combat crime, how can they advocate that way?
But the chance for someone to get caught if they do illegalities are much higher than for someone that do illegal acts online or by using cryptos. I don't believe there are countries that are free from crimes but every country should have at least a few crimes that occur from time to time. They are not blind to not noticed it.
Traditional or non traditional money can't do anything to solve the crime but avoidance of crime should start to the people and to their governments. People must be knowledgeable and take extra care of what they are doing, also the governments should enforced stricter rules and won't give an exemption for every criminals that they caught.