I assumed you would know the details. Printing lead to printing of bibles in the vernacular languages of Europe, which lead to the lay people starting to have their own opinions on the meaning of the word of God, which meant that when a certain M. Luthor objected to some religious practices of his time that got popular support, which lead to war.
That war, lead to the employment of printing as a propaganda tool. People tended to believe printed stuff as true, often accepted these propaganda pamphlets which fuelled the religious wars of the 16th and early 17th centuries.
The Malleus Maleficaurum, a book written by a pair of ex Dominicans, (whom, if memory serves, were thrown out of the Inquisition for bad behaviour) was widely believed by secular authorities as the correct way to find out witches and is probably directly responsible for the deaths of tens of thousands.