Bitcoin's anonymity is really a great characteristic. It enables users to use BTC in any transactions with nearly no traces. But is this really a good thing? Let us consider utilizing bitcoin in a negative way. Since bitcoin is considered currency, there is no doubt that a person that needs money will not reject bitcoin even if it involves unethical or illegal act.
Due to the anonymity of bitcoin, some uses bitcoin in a negative way [citation needed]. They can easily use bitcoin in paying others to commit crimes. They can even use bitcoin in bribery and/or money laundering. This characteristic of bitcoin are abused [citation needed] and it will never end well.
For the case of terrorism, terrorist can easily purchase weaponry from other country. With the use of transaction using bitcoin, authorities will have a hard time tracing that transaction thus, will give advantage to the side of terrorists.
This is not an impossible scenario. People can now use bitcoin in any way they want to. It's inevitable.
Indeed, there are people who are using bitcoin for bad things. Pretty bad things in fact.
If you ask anyone on the streets what they think of bitcoin one of the top responses they'll probably give is money laundering, fraud, buying drugs on the deep web, prostitution, all these illegal things that people do.
But there isn't really anything we can do about it.
Terrorists are able to use fiat currency as well. And most probably do due to the fact that bitcoin is still underappreciated around the world especially in areas where internet usage is still low. If they choose bitcoin to operate on, then that's like choosing cash. People use cash to buy groceries, and people use bitcoin to buy legal things as well.