Can't deny the fact that bitcoin is used in many crimes worldwide, especially in darknet for drug or arms trade. Even criminals were using it for internal transactions! For money laundering, bitcoin and XMR has become a major tool for the criminals. Recently a Chinese man was caught in India who has been using bitcoin since last 3 years to launders millions of dollars. So this is a real threat!

Probably that's one of the major reasons why bitcoin is still not legal in many countries. But sadly, there will always be such people around us who will make illegal use of anything. These can't be uprooted, unfortunately!