But if you get your bitcoin from the dark web, you need, (or should use) a mixer to disassociate your self from any BTC you purchased. They also recommend you consult a lawyer first. It all sounds very nefarious on the bitcoin user's part.
On the other hand they mention the U.S. Army and NSA are are tracking cryptocurrency users by analyzing transactions, which make the government sound more nefarious and sinister
Unless you're a blockchain analysis expert it is hard or even impossible to determine if yours coins are clean or not. Bitcoin is so mixed that there is no absolutely clean coins (maybe those fresh mined).
Why should US Army tracking cryptocurrency? However NSA is working on bitcoin case at least from 2013 as revealed in the documents released by
Snowden. Even then they have very powerful tools (Xkeyscore, Oakstar, Monkeyrocket) to track bitcoin users, and after 6 years these tools have become even more powerful.