I'm not saying that not wanting people to be blown up is uniquely capitalist. What I am saying is that people seeing the _value_ of their actions as whether they encourage or discourage good or bad behavior is very capitalist. It's also arrogant, self centred and intellectually moribund.
Except that it didn't. Anarcho-primitivism was fringe, and it's still fringe. Maybe you could say that it changed the way anarcho-primitivists thought about stuff a little bit, but that could've been achieved without murdering people. It doesn't take much effort to "get a message out" to a tiny community of intellectually-curious thinkers.
Considering everything fair game regardless of it's origins or consequences feels extremely capitalist to me (well probably libertarian - but I don't feel like capitalist is a particularly well defined ideology).
It would be totally unfair to criticise a piece of anarcho primitivist writing by saying "I'm not reading this, this is what Ted Kaczynski believed".
But Kaczynski murdered people to get his ideas read - I don't want that to be a way that political ideas make it into the mainstream.
If the ideas are good enough they can stand on their own two feet - plenty of not unabombers have written similar stuff so why not have articles about them?
Also I feel like the majority of political systems discourage letter bombing as a marketing technique - it's not unique to capitalism.