This video by Pete Eyre of Cop Block is valuable on its own, but I think it also highlights the different premises that people are working from when talking about aggression.
A person’s act is aggressive depending on what the person has a right to do. For example, a person breaking his or her own car windshield has a different moral claim than if he or she were to break another person’s windshield without proper cause. From the FBI agent’s perspective, anyone who does not submit to the government’s edicts is committing aggression (fraud, I suppose) by not abiding by an implicit agreement to follow the government’s laws.
I am not saying anything Pete does not already know, but it is something I try keeping in mind when talking about such highly conceptual entities like rights and the non-aggression principle.