I love this question. It makes me chuckle because everytime, the answer is invariably "yes" - regardless of the book. It's all about how you answer a "should" question. Any question involving a "should" ought to be dealt with in terms of consequences. Will the outcome yield a positive, negative, or neutral outcome? Will I like it? Will I learn something? Will I get an idea for something? These are all positive outcomes. Not liking a book is more of neutral outcome, since I've still gained something from the experience and am not somehow lessened because of it. Even a bad book gives you the possibility of learning something from it or perhaps getting an idea for something better. Negative outcomes involve diminishing resources or possibilities for yourself and/or other people. Will reading this book stop me from getting into college? No. Will it bring harm to me, or someone I love? No. Negative outcomes may follow from the political or legal context of particular books (as in banned books).
Once you've identified all the probable outcomes, the next step is to weigh their severity and likelihood. If the potential for a positive outcome outweighs the potential for negative outcomes, then the answer to "Should I read this?" will be "Yes". When you say that someone should not read a particular book, you are saying that there is virtually no chance of them gaining anything from the experience.
A completely different question, and one that I struggle with all the time, is "Should I read this book right now?" For a lot of books, the answer to that question is "probably not".
