I see the concern, but this has nothing whatsoever to do with where the books come from. It's no justification for prohibiting books from all but a few approve

I see the concern, but this has nothing whatsoever to do with where the books come from. It's no justification for prohibiting books from all but a few approved vendors, prohibiting used books, prohibiting e-books, or eviscerating prison libraries. There may be other arguments for these other prohibitions. But the coded-message argument is completely without merit.