A Wikipedia study of readership show that people largely abstain from reading certain articles about terror groups after the NSA mass surveillance revelations of 2013, in fear of being redflagged as potential troublemakers. This is an entirely new form of self-censorship, and the media reporting on it has failed to see and explore this new form of self-censorship that has developed in fear of being redflagged in a new technical landscape.
The classic self-censorship is refraining from speaking out. When speaking out gets you in trouble, formally or informally, this interferes with freedoms of speech and expression.
The KGB created a second form of self-censorship that attacked the freedom of association.
Imagine you’re holding a (physical) encyclopedia in your hand, and you’re afraid of reading certain articles, self-censoring your behavior to look away from them. If you were reading a book, that you were avoiding certain pages. This is what the Wikipedia study shows is happening. This is self-censorship of the freedom of information, and it’s something entirely new and destructive that the NSA has caused.