Not true though. Christian thinkers such as Augustine of Hippo, Anselm of Canterbury, Thomas Aquinas and the scholastic school of thought the latter two represented upkept very intricate forms of reason based thinking, even through the Middle-Ages. Also people before and after them who were vital to the western thinking such as Socrates, Aristotle, Descartes, Mill and others considered the existence of God to be necessary. Even Kant in all his iconoclastic quest for empiricism and consequentialism still held the belief that there is some kind of deity out there.
And these are only western examples, Arabic, Indian and East-Asian cultures had a variety of spiritual beliefs (in spite of often coming to completely different conclusions about godhood compared to western Christians) despite their own societies and schools of thought being very advanced in their own right.