Do books really make people unhappy?
Well, I think this question derives from the central conflict in the book, as well as the idea that reading brings knowledge. Reading expands your mind like no other activity, & allows you to apply what you've read to your own life & creations. Yet there is the old saying "Ignorance is bliss." Essentially, people are happier when they don't have knowledge of terrible pain, or hurtful truths. Consider the character of Charlie in Flowers for Algernon. He gains intelligence, but with it knowledge of the cruelty and manipulation people can perform. This would suggest that one is happier without knowledge, but how can one be truly free if one doesn't know? How can one truly state happiness if they are not aware of truth?
There is a similar situation in Fahrenheit 451. Bradbury begins the story with "It was a pleasure to burn." This suggests that Montag is happy when working, and is content in his life. Yet later, when Clarisse asks Montag if he's happy, he can't answer her. If we consider the end of the book, we can't argue that Montag is happy (watching the city destroyed by a bomb, & knowing his wife is dead probably wouldn't be conducive to a content mood), but we also can't deny that he is more free than he's ever been, & that with independence comes a certain satisfaction.
So, I would argue that books are essentially neutral. One can be happy or unhappy when reading, but it is entirely dependent on the person themselves. I suppose it is contingent on how you let yourself be affected by what you read. But inherent in this is the idea that truth can bring pain, & thus cause unhappiness. Yet it can also bring freedom and power.