Extortion in the form of ransom-ware, theft in the form of stealing bitcoin from exchanges. (Mt. Gox, and a more recent case.)
Legitimate businesses in the bitcoin space make small margins on each trade/transaction/etc. (Drug dealers are obviously a little different, but they are in the business of unlicensed pharmaceuticals, not the business of Bitcoin.)
Thieves, on the other hand, will take the whole thing, and run.