As an example of older (and perhaps suspended, though triggering a visit off of communist books seems so 1980s) program, I recommend reading
Surveillance in the Stacks, which is about the FBI's Library Awareness Program.
Here is a historical recap of the national security argument for reading habit surveillance. And
here is a page at the American Library Association web site that compiles information on this topic.
I want to be clear that I am not bringing up all these other examples in an effort to dilute this incident but rather to show that it is a long-standing issue and that usually only creeps into the pubilc conscience with specific incidents and then quickly fades.
Here (facetiously) is the horrifying thing for me, that an academic library system as good as Dartmouth's wouldn't have a Chinese copy of the book on site and the student needed to use ILL to get a hold of it.