Young adults are still children and children should not be exposed to difficult themes in Young Adult books.
In 2017 Angie Thomas' "The Hate U Give" was banned in a school in Katy, Texas after a parent complained due to the story's inappropriate language and sexually suggestive content.
The book has received other complaints from adults who felt it was not appropriate reading for young people because the "f" word is used over 89 times and there are references to drugs. In addition to this, there are implications that "The Hate U Give" presents a rebellious anti-police sentiment that sends out an irresponsible message to young people. 
The difficult themes in young adult novels take away a young person's innocence.