because of technology, bitcoins can be traced through the address but can not be known who the owner is. maybe this is what causes the criminals to use bitcoin as an intermediary for crime. but that does not mean the guilty bitcoin in this case, but the irresponsible people who are already using the situation.

for illegal issues, must be dealing with the government. every government wants everything in its state to be controlled by the government, "perhaps for the sake of the convenience of its people", but bitcoin can not be controlled by anyone, maybe that is one reason why it is considered illegal.