My camper asked if Harry Potter (“the world-class 7 book series talking about magic and a young boys adventure through school and conquering evil” as she described it), would fall under the category of books that are Assur?
This and other books that fall into this category (fantasy novels) are not proper for Jewish reading. Particularly if it discusses magic, witchcraft and other forbidden behaviors. Moreover, the morals and values gleaned from this series are inconsistent with Torah.
The Alter Rebbe rules (Shulchan Aruch Orach Chayim 307:30) that it is forbidden to read such books not only on Shabbos but even on the weekdays due to prohibition of מושב ליצים (a platform for jokers).
Reading secular books has a profound influence on one’s thoughts and thus secular books which are contrary to Torah can be damaging to the neshama. One can instead read kosher Jewish novels which are in great abundance today.