The reason is covered in the article:

> I've deliberately avoided mentioning any specific heresies here. Partly because one of the universal tactics of heretic hunters, now as in the past, is to accuse those who disapprove of the way in which they suppress ideas of being heretics themselves. Indeed, this tactic is so consistent that you could use it as a way of detecting witch hunts in any era

Talking about PR[1] isn't wrought with intellectually-dishonest landmines in the manner that it is for talking about what Graham terms "heresy-hunters". This is also obvious to even anyone who's paying a mild amount of attention to the cultural changes he's describing.

[1] the topic of "The Submarine", for those who are unfamiliar