Answer:
The correct answer to the question: What is the author´s purpose in this excerpt, is, C: To explain why those in favor of banning books believe doing so is positive.
Step-by-step explanation:
This answer can be explained by the text itself, where the writer literally is explaining the why of banning, and the reasons behind this particular action, against books, and other media, that could harm younger people. TO begin with, the author does this by first stating the history of banning, and especially, the reasoning that was used by authorities to take such an action. Later on, the author continues by moving from history into the present and againt states the reasons why nowadays authorities again ban books, showing that in this way, they are doing something good for the future generations. This is why the answer is C.