The dark web is the World Wide Web content that exists on darknets, overlay networks which use the Internet but require specific software, configurations or authorization to access. The dark web forms a small part of the deep web, the part of the Web not indexed by search engines, although sometimes the term "deep web" is mistakenly used to refer specifically to the dark web.
Every affair in the dark web will use Bitcoin as a method of payment. In the dark web there are various illegal businesses such as the sale of illegal firearms, drug trafficking, assassins and hackers.
What are your thoughts on this Bitcoin abuse?
A small percentage of bitcoin is used in the dark web for illegal purposes and then for ransomwares, money laundering, and other financial crimes. Why bitcoin is being used for all these illegal purposes, because it is pseudonymous, still not anonymous. The government recently took down Alphabay and Hansa and then the BTC-E money laundering case.
It has been quite some time since Bitcoin is being labelled as a currency used by criminals. From a legal usage point of view, bitcoin is secure, transparent, decentralized and protects your privacy, but still trackable if the government wants to and sooner or later governments would be going hard on people/businesses using bitcoin for illegal purposes. So I don't think bitcoin would be a popular currency for illegal usage in the future.