There are a variety of reasons why people choose to read books. There is no rule that people should only read books that are of benefit to them. Nevertheless, I contend that there are some books that are out the other side of a neutral effect and detriment the psyche of the reader.
This effect can sometimes depend on the current mental state of the reader. For example, if you were generally prone to depression and were going through a particularly tough time of your life (especially if you were feeling a bit middle-aged and under-rewarded) I wouldn't launch on a Graham Greene binge.
Then there is the entire genre of crime. How can a literary diet of torture and suffering, often against women and children, improve your view of human nature? Ah, some say, these are generally moral tales where ultimately good triumphs over evil. That alcoholic, dysfunctional, slumpy detective will eventually catch this evil perpetrator. The fact that the detective (and reader) will gather psychic damage from their entry into the world of an imaginatively violent psychopathic killer is considered of secondary effect to the edification of the reader from the ultimate acquisition of justice, no matter how imperfectly acquired.
Not only do I doubt the maths of this equation, but I think a cumulative degenerative effect is achieved by the regular application of books of this genre. Repeated doses chip away at a reader's generally positive view of the fundamental nature of humans. Psychopathy is apparently quite rare, but it is common as dirt in these types of novels. How can you regularly read them and not dwell on the evil that lurks in the hearts of strangers?
I put it in the same category as the increase in reporting of violent crimes leading to people being convinced they are more in danger of violence then they have been in the past. It is not the incidence of violence that is increasing, but its popularity as a form of journalism.
Another generally degenerative class is the classic romance novel. It conditions women away from a realistic view of relationships in the same way that pornography conditions men. This drift from reality means neither party is in a healthy state to engage in a sensible relationship involving give and take. (I can't even be bothered talking about low-end erotica because the thought of all that submissive behavior gives me the screaming erks.)
Finally, I should like to tell you about a novel I just started by Philip Roth. I read Portnoy's Complaint in my teenage years. At that time it seemed a novel that was 90% about masturbation was new enough to have some merit in its elucidation of the sexually obsessed mind of a teenage boy. I started reading a relatively recent Roth novel yesterday. While I only read the first and last chapter, it seemed unlikely that the sex life of the novel's protagonist was going to be omitted from any intervening page. It stuns me that in the 30 years between these two works, there had not been any increase in the maturity of the main character or their obsessive interest in sex generally, and masturbation specifically. Are all his other novels on the same topic?
Frankly, I don't care to know the answer. Whatever mild sexual thrill may be obtained from this stuff is well and truly counteracted by the exposition of a personality so immature and destructive. People's own experience of sex can fuck them up without reading 400 tedious pages of someone else's attempts to destroy their own life and the life of everyone around them with the pursuit of continuous, dirty sex.
Sigh. Possibly I should have written a blog about the range of possible edifying effects of reading. I may need to save that for another time, but please, consider asking yourself, "Is your reading making you a happier person and is it strengthening your view of the nature of humanity?" If the answer is a big no, then why are you doing it, and would you be better off seeking out something with a more neutral or positive effect?
Or not, you choose.