Dark web markets are one of the biggest reasons why Bitcoin came on the black list of many. Some people still think if Bitcoin is used for illegal goods and services it's illegal itself.
Also some think in a wrong way that tsking down illegal dark web narkets and putting their creators and runners into jail it's an action against Bitcoin and cryptocurrencies. But that isn't so and to my opinion someone who runs places where you can buy drugs, weapons, child pornography and similar deserves to be punished and that will not harm Bitcoin, just the opposite.