An easy mistake
It is an easy mistake for a Christian to make: go to the library or a reliable secular website when they need a book on marriage, bringing up the kids, depression, whatever. We have been conditioned to seek information in this way.
But this is a fatal mistake for a Christian to make for one big reason......
The world has messed up its thinking
According to Scripture, unbelievers can't think straight. The moment a man or woman suppresses the knowledge of God, they mess up their mental apparatus. This is how it works. Out there in the world of creation there are numerous evidences for God. Complex things demand a Designer; beautiful things demand a Painter; immense things require a Power. Inside our heads we have been supplied with a mental apparatus which works out cause from effect, all very naturally. Put these two together and the mind inescapably comes to one conclusion:
Evidence from Creation + Internal mental "cause and effect" reasoning => GOD
Today we are spoilt for choice when it comes to evidence from Creation, there is just so much of it.
Now, if a human mind suppresses this normal cause and effect process, when it comes to creation and God, it messes up all the reasoning of that human mind.
This is not at all surprising - if a man makes such a big mistake in his reasoning at such an obvious point, how can he think right anywhere else? If he does the first button of his shirt wrongly, how can he expect the rest to be right?
This is what the apostle Paul teaches in Romans 1. The human mind that deliberately denies the massive and inexcusable evidence of God's existence simply can't think straight on anything else:
"....their thinking became futile and their foolish hearts were darkened."
This, sadly, of course does not stop them from thinking they are wise:
"Although they claimed to be wise, they became fools."
But this teaching of Paul's, that a mind which denies the existence of God knocks out all of its reasoning processes, has very large implications for all branches of human knowledge (I am here referring to secular studies).
Does that mean that everything an unbeliever says is wrong?
No, because 'common grace' teaches that God preserves some truth in the world (this world is not hell) so that Paul can quote from pagan thinkers in Acts 17, approvingly. The least 'corrupted' truth is likely to be found in hard subjects such as physics and chemistry where the subject is matter, rather than God, man or morality.
Much truth will be distorted
But the moment the world begins to talk about God, morality, or human beings, we are to be completely suspect of all its teaching. Common grace means the world will sometimes stumble upon truths even in this area. John Gray in Men are from Mars, Women are from Venus, for example, stumbles upon the fact that there are some real differences between men and women. But we could not trust secular thinking on the history or origin of the world, right and wrong, sexuality, the future, the supernatural, miracles, and so on. In all these areas its thinking will be foolish.
The Bible or Christian books
The place to go for all these matters is the Bible and to Christian authors. We must teach our churches and children to have a healthy mistrust of everything taught at school or university. It may appear wise, but it is, in point of fact, foolishness. And we must continually renew our own minds with God's truth:
"Do not conform any longer to the pattern of this world, but be transformed by the renewing of your mind." (Romans 12:2)