yes it may be but i personally have no idea, to me as bitcoin is a new born currency and still hardly 1% of the world population will be using bitcoin,and the one percent are those people who have good command on computer and internet, and well educated, so i can say that the illegal bitcoin users will be negligible, and i will like to add that most of the people of the world will be using the most popular currency of the world which is almost in every country is applicable, therefor USD is the best option with them using for illegal activities.