Because of bitcoin does not give public details of people who make transaction with it, some people do say it promote crime. People needs to understand one of the features of bitcoin is freedom that anybody can get access to it, it does not discriminate. The privacy features of bitcoin is very important to humanity, which I know one of its advantage is for safety by using cryptography that makes all transactions safe and encrypted.
Privacy in transactions of bitcoin is much important, if their was no privacy it would have cause several criminal attacks. For those who think bitcoin encourages crime because of hiding public data of users don't understand the importance of bitcoin being private. Before bitcoin started existing monetary crime have been existing. Bitcoin is not a reason for monetary crime, bitcoin is just for everyone and does not discriminate but accept everyone.
This is a story that has already been debunked several times: first of all bitcoin is not completely anonymous, every single transaction, every single movement is stored on the blockchain and therefore it's possible to follow the coins. Even when mixers are used. There have been some cases where the FBI managed to follow stolen bitcoins despite the thieves tried to do everything to hide them. On the other hand cash is way better for criminal activities.