Probably, any technology can be used by criminals to carry out crimes. For example, to give bribes in cryptocurrency, pay for drugs, weapons, etc. After all, there are completely anonymous coins. That's where the danger lies. On the other hand, there are much more positive aspects.
Everywhere there are negative moments. The same cash, too, because anonymous. They do not provide information about who held them and who gave them for what. So this is a variation of "cash" in the virtual world.