Language defines thought, and thought informs behaviour. To use the two words in the same sentence like that is to treat the two concepts as equivalent, and to promote their equivalence in future.

There are, actually, many similarities. Both groups of people defy social norms and seek publicity in the course of acting out grievances with the establishment.

Activism and terrorism are often one and the same. I don't think it's unfair to describe 9/11 and similar terrorist attacks as forms of activism — not that this in any way justifies the attacks — nor to apply the 'terrorism' label to many self-described activists (e.g. Anonymous with their computer hacking)

Terrorism and activism are both political, but I wouldn't call terror attacks activism. They have different means and execution, even if they both strive for political change. Not that this distinction is helped by how politicians love to paint activists as terrorists for political purposes.

OED defines activism as: "The policy of active participation or engagement in a particular sphere of activity; spec. the use of vigorous campaigning to bring about political or social change."

Most contemporary terrorists (Islamic extremism being the most salient example) are not terrorizing people for the fun of it. They want to bring about political or social change. The 9/11 terrorists objected to U.S. foreign policy, specifically its support for Israel and continued presence in Saudi Arabia. Terror is just a campaigning tool.

I don't think politicians are too far off the mark when they describe certain contemporary activists as terrorists. As I say, it's a very thin line, and plenty of contemporary activists resort to terror tactics.

You are clearly a philosopher of language and thought and so I am reluctant to contradict you, but it has been my experience that the construction "A or B" is more commonly used when A and B are non-equivalent. Perhaps you're thinking of the situation where B is an acronym inside parentheses, as in: random access memory (or RAM).

Applying that experience to the sentence in question (and probably because I am not as vigilant as you in detecting attacks against freedom), I read it to distinguish activists who would perhaps be wearing a faux-bomb as protest against security measures from terrorists who would be wearing a real bomb watch.

I look forward to your well reasoned response.

I'll take a stab at this. Many times "A or B" are used when they are different in some way, but both have something in common. For example, an alternative to driving to work is to bike or walk. It's cold out side, so I need a jacket or sweater. Can you call or email me when you get the results. In all these cases, the A or B construct is used to tie together items that share something (alternatives to driving, cold-weather add on clothing, and methods of communication, in these three cases).

I'm confused, why would a political activist in particular be more likely to carry an improvised electronic device?

It happens all the time. There are plenty of people who just want to create a scene, cause a fuss, make life difficult for security staff, etc.

Journalists have also been known to test the limits of airport security, taking suspicious items on board planes or gaining access to restricted areas, then reporting on the associated security lapses.

To cause a fuss and make a point about the TSA.

isn't the implication "he's not a bad guy" rather than "he's not either of these two groups, one of which would reasonably explain his behaviour anyway"?

i think that's what worries people (and me). that his own lawyer, apparently defending him (not just explaining, but holding him up in positive contrast), seems to be saying, "look, he's not one of these problem groups". and in that sense, as a "problem group", activist and terrorist are presented as similar.