Wiener - I disagree with this: "Yes, a middle schooler should have the maturity to know when to read and when to walk away. The kid clearly had this ability himself. He knew he didn't want to read it. Except instead of walking away and saying "I don't want to read this so I wont," he insisted that no one else read the book either."
My kid is a middle schooler. I know his friends. I would not trust these kids to basically raise themselves, as you are arguing. They make terrible decisions all the time. They need adults to put limits on them and teach them manners and good behavior.
Your age is only relevant if you are a middle schooler yourself, making a pitch for adult freedom. If that were true, then I would better understand where you are coming from.
So is the kid a wiener for 'telling on' the library? I don't think so - because he was right. That book should not be in a middle school library. It is generally a good thing when adolescents ask their parents for advice and guidance.