I don't think that this is true. Bitcoin and other cryptos are mainly used by investors due to the high daily price change, the easy of using them and from those who want to hide their funds or make international payments. I believe that less than 0.1% of transactions belong to criminal activity. Don't forget that criminals don't care about currencies. You think that a criminal can't use USD or other currency to make a transaction? Except if you mean as a criminal someone that wants to hide his money from tax authorities.