Holy books are outdated
Most holy books were written hundreds or thousands of years ago to address issues that existed at that time. Circumstances of the modern age are quite different and scripture is now outdated and irrelevant.
Theists may argue that the Bible contains a timeless message. 
- "For example, the Bible has a great deal to say, directly or indirectly, about marriage, divorce, remarriage, alcoholism, substance abuse, stress and depression. It speaks to man's most damaging emotions, such as anger, guilt, fear, doubt and anxiety and condemns dishonest, immorality, arrogance, greed, selfishness and obscenity. [...] No other book ever written comes close to the way in which the Bible speaks to life in the twenty-first century."
The problem with this is it implies that holy books cannot be improved upon and the social context is unimportant in interpretation. This attitude is an obstacle to tackling social problems and other issues of our age. They also teach incorrect scientific ideas, the inferiority of women and backward social systems. Most holy books, including the Bible and the Qur'an, do not forbid slavery, racial inequality, marital rape or provide basic political freedoms. They also have an obsolete view of sexuality. Scriptures also fail to address many areas, such as most of medical ethics or AI ethics. In short, this type of backward looking religion is harmful.
Apologists are often cherry picking the Old and New Testaments to what they consider to be useful. To say it is useful to resolve all social problems is itself harmful. Christians generally don't follow the principles of the New Testament and the teachings of Jesus, so they say with their words that it is relevant but by their actions they say the opposite.