It is worth remembering that Nelson Mandela was called a 'terrorist'.
The term is so politically charged and ill-defined that I don't really like using it, I prefer terms such as political violence, sabotage, assassination etc., many of which fall under the umbrella definition of 'terrorism'.
All labels can be misused and mis-applied- see the near meaninglessness of 'fascist', 'communist', or 'socialist.' It doesn't mean those words don't have actual meanings.
While there is no single global definition of terrorism, since it is a loaded term that people love to abuse, there is a unifying point of it that distinguishes it from political violence, sabotage, assassination, etc., which may or may not overlap: an intent to create public fear as an means in and of itself to force a change in policies.
Political violence doesn't always entail intimidation. Sabotage doesn't necessarily create fear rather than accomplish it's own objective. Assassinations may never be known. But terrorism is a method directed towards public perception to pressure groups as a whole.
One of the difficult areas of defining terrorism is - can states be terrorists?
If not, then aren't ISIS, by definition, not terrorists, but a nation we are at war with?
'Terrorist' is an individual, not group, identifier. The answer is 'no' because organizations are not individuals.
'Terrorism' is a method of operations. 'Terrorist' is someone who is using those methods. Groups that employ terrorism are terrorist groups, or, if states, state-sponsors of terrorism.
Whether we are at war with ISIS is a separate issue, because no one recognizes ISIS as a nation, any more than the warlords of West Africa in the 90's. They're a group of people with guns who control land, which does not a nation make.
At that point, isn't everything bad done by a state 'terrorism'?
Only if it's done to other states with an intent to use public fear to change policies. Libya supporting the IRA and bombing German clubs frequented by military would be examples.
Utilizing terror on your own population as a means of social control is bad, but it isn't terrorism- the fear isn't serving a political purpose of forcing the group (the state) to change it's policies. It is the state policy. We can call these reigns of terror, but it's a separate form of violence than the practical practice of terrorism.
My point is that you shouldn't focus on the strict definition of what a person's actions are, but on their motivations, their targets, their effects and the greater context in which they are performed.
In all those regards, Anders actions come Act 3 are terrorism. His motivation was to inflame tensions, including fear and anger, to spark a conflict. He chose a symbolic political target that didn't even have effective control over the military target he wanted. The assassination and devastation created the fear and anger to polarize the political environment to catalyze a simmering secretarian conflict. And the context was of a city that had undergone years of secetarian strife and tensions of various sorts, and which was in the midst of a terror as maleficar roamed the streets and deliberately seeking to sow chaos.
In modern democratic societies, where people can have their say, freely debate issues, then political violence is a terrible thing. However, in a society where people have no such liberties, political violence may be the only action which an individual can take. So I don't think Fenris is all that bad (even if he's my least favourite of all DA companions) because, well, look at the society he's in. Playing by the rules would get him and his cause (emancipation of slaves) nowhere. Whereas I consider Anders to be a terrible person, because his actions targeted innocents, and created a level of chaos that was just awful for everyone.
Fear, violence, chaos, and instability are horrible no matter where you go. Rationalizing it on grounds of 'well, they aren't free, so it's all good' is simply a short-cut to justifying it on personal perception of how much freedom is 'enough,' while also ignoring the existence of alternatives.
Terrorism isn't the only form of subversion, or defiance, or resistance. It's not even the most effective means of promoting social change.