Anything excess than its limit is very bad and dangerous.
Reading is a good habit unless it is for the purpose of learning. When someone starts reading for pleasure there are lot of possibilities of bad effects. Generally, books/comics/magazines of non-fiction are meant for learning purposes. All the fictional books or comic or magazine are for the purpose of entertainment. Reading for pleasure in a particular schedule is not bad but getting addicted to reading is very bad. The fictional topics also involve romance, porn and much more. The addiction of these type of topics is far more dangerous than getting addicted to drugs. Some people get so much involved in reading that they forgot to concentrate on other things in their life. They are completely detached from the society and they remain alone. This is not a good thing for any person.
So reading should be checked out in the case of an addicted person. Yes, reading book is indeed a very good habit there is no doubt about this. But, there should be a certain limit in reading. Unless there may arise a very complicated situation. The person may live in the fictional world with the fictional character of the book.