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.
I share the same sentiments as above. That is why some countries do not support the use of Bitcoins because it has successfully penetrated their respective jurisdictions without requisite regulations.
I really think that Bitcoins can go a long way for the better, however, its proliferation should submit to a State regulation in order to do away with illicit businesses that come with it. Just like a normal currency which is developed as a means of exchange but is still widely used as means to create crimes, Bitcoins also have the same dilemma. Thus, the only answer is a sound regulation that will address this issue. The aforesaid regulation cannot be expected to do away with all the negative intricacies but will only somehow eliminate the unacceptable side.
This much like the barrier that hinders certain countries to acknowledge bitcoins. Gaining anonymity on bitcoin transaction gives advantage to those terrorist who were collecting money through illegal means. This means that we would have difficulty to track where the funds came from and where it would be send.