Anything could be done to anything. Fiat can also use for such things as child pornography. It is all over the world but people usually do it for money and no one can stop it.
ever since in the history of bitcoin. we know that there's a site that the bitcoin is used for the illegal activities like transaction of illegal drugs, illegal trafficking , illegal fire arms. but not only that, there's also an child pornography and a people to hire to killed one people. this is called deep web. and this site are mostly used by the bitcoin.