I don't think the Unabomber or Anonymous fits in the same policy discussion as IS or Al Qaeda, because I think these problems suggest very divergent courses of policy. Every time we have to make caveats to our category, every time we must exercise discretion in interpretation, we will find our construct proportionally less robust.
Imagine a government rule which authorizes military action against IS, cartels, or Al Qaeda, including assassinations and characterized by an absence of legal process. Whether or not I agree with this rule, I can accept that it is sensible and potentially productive to at least talk about. I can accept that these groups have common characteristics which behave consistently following military or civilian interventions, thus permitting policy generalizations. I can also see that there is an intuitive connection between the solution and the problem.
What is hard to accept is that Unabomber and Anonymous should be on that same table for discussion, because what the overinclusion of these groups do is move the line of justification to remove legal process a little closer to home, and a little more into the realm of capricious discretion. It's hard to accept that some domestic terrorists are anything like an organization that has revenue streams, human resource management, infrastructure, administration, a paramilitary force, and so on, and so it's hard to connect the solution to the problem.
Of course, behind all of this is the assumption that terrorist organizations are so mighty that they have graduated beyond the class of criminal and into sub-state actor, and that ordinary civilian instruments are totally inadequate, and that military solutions are the only effective solutions.
[1] http://www.theguardian.com/commentisfree/2013/apr/24/boston-...
[2] http://www.theguardian.com/commentisfree/2013/mar/18/david-f...
Terrorism describes the strategy of pinpoint deployment of outlandish violence to coerce policy by generating fear. That's one strategy used by paramilitary organizations, but so is "seize and hold territory" or "persistently disrupt supply lines". Islamist terrorists don't target JFK airport in the hopes of disrupting our military supply lines. They do it to provoke the US public by creating fear.
Having said that: I'm not sure what coherent public policy objective is served by singling out "terrorism" from other violent crimes. At the level of law enforcement, criminal violence if criminal violence whether it be in the service of a bank robbery or a radical animal rights protest.