USD used many illegal activities I think because it is main currency in the world to be the benchmark currency of the countries in the world, so widely spread. USD it became many used for illegal activities like terrorism and illegal war because of its spread widely so that it can be reached by people who are not responsible. The use USD for legal or illegal activity actually depends on each person who uses that can not be avoided and unruly spread.
That's right, currency is basically a tool and don't have an intelligence so even some currencies being used for illegal activities it's can't be concluded as those currencies were getting involved into crimes and after that it's prohibited, some media sometimes just too hypocrite and always making the images of their opponent looks bad by spreading bad news about it,but at the end it's just a currency
Yes, I really like what you say that currency is basically a tool and don't have an intelligence. That is true, for what that currency will be used quite dependent on the person using it. So we can not fault currency if it is used for illegal activities. Spreading USD high and become a benchmark currency worldwide makes the USD vulnerable be used for illegal activities. It's don't much different from the bitcoin that could be used for illegal and legal activities.