My best guess is that he means the author's characterization of the people themselves. The Enlightenment produced the modern scientific revolution, which arguably led to the largest increase in quality of life since man walked the earth. It also produced a focus on reason and empiricism, which ultimately led to modern civil rights movements and subsequent legislation. When the author attempts to discredit these people's contributions by attacking their character via unfounded accusations of misogyny, it significantly harms their credibility.