I strongly agree with your opinion that many criminals use bitcoin, which is why the government does not legalize bitcoin because it is difficult to control bitcoin transactions, but it is not a crime created by bitcoin, but the community and the people themselves who use bitcoin in places wrong. Not only with bitcoin with fiat money was a lot of crime.
By using bitcoin, criminals easily make transactions without being noticed by anyone though the government. the transaction here can not be traced, therefore the government does not legalize bitcoin.