Bitcoin is the easiest form of currency to accept, so clearly it's going to be good for those who want to avoid the whole process of verification with bank, specifically criminals for that matter. If banking isn't in stable conditions (for example Greece), then Bitcoin is absolutely dire. Bitcoin helps those unbanked, and those with "corrupt banks".
I think the association with criminals and bitcoins has really affected the image of bitcoins. I wish there was something which could be done to stop access of bitcoins to people being involved in criminal activity. With all the advanced technology, all the tracking systems and algorithms, is there something which could be done to stop such malicious activity or we let it go just because it brings in more trade? :/
Bitcoin combines cryptography and a peer-to-peer architecture to avoid a central authority rather than how digital currencies such as eGold and WebMoney operated, law enforcement agencies have more difficulty identifying suspicious users and obtaining transaction records and getting criminals under their handcuffs. This has definitely screwed up the scene for bitcoin a little.
There have been so many hacks and attacks with the involvement of bitcoin as either theft or asked as ransom. A recent attack happened recently. The attacks took place in two stages. An initial DDoS attack was followed by threats of further and more severe attacks if the targeted websites did not complete bitcoin payments. If you want to read more bitcoin crimes, here's a link: http://www.coindesk.com/bitcoin-crime/
