These folks know exactly what they're doing. I've worked with one of them -- he saw it as a plus that he's slowing down drivers and blocking traffic and would cycle in a way that made it impossible to pass him. He framed it as environmental activism.
In more than one other sub-thread here, people have offered variants on the theory that some drivers are hostile toward cyclists and/or more likely to notice cyclist transgressions because those cyclists constitute an out-group and that's what we always do with out-groups. "Treating them differently just because they choose to live a bit differently" is the most recent version I saw.
Well, that cuts both ways. A certain subset of cyclists treat anyone in a car, or indeed not on a bike, as an out-group. They notice transgressions more, deny the out-group's right to do what they're doing, etc. It's not activism. Positive change is not the goal. It's just venting their own unresolved anger and frustration. If the putative cause of their complaint disappeared, they'd miss it ... and then they'd find a new "cause" to be anti-social about.
The different treatment is injury and death vs slight inconvenience. It's an asymmetrical arrangement in favor of the car for any kind of two wheeled conveyance. Or are you fearful of ten-speed riders traumatizing you by impolitely smashing up on the windscreen instead of politely disappearing under the wheels?
You are not wrong though. It just is not a defensible position. You won't be the one who suffers.
You're missing the point. What matters is that GP's friend had used "activism" to describe acts of simple spite or revenge, and the label does not apply. Such behavior stands in the way of real activism. Perhaps you feel the spite is deserved, the revenge justified, based on the level of potential consequence. Your use of hyperbolic imagery and character assassination suggests that you might, and I might not even try to dissuade you ... but don't call it activism. Words have meaning, and a potato is not a pear.
It's the cyclist equivalent of rolling coal.