Having spent several years of my life as an Enlightenment scholar, I never cease to be be amazed at the many ways the Englightenment is misunderstood and misinterpreted. Which Enlightenment is he talking about: German, French, Anglo-Scots?
In one sense, the Enlightenment is the problem, and IMHO, in that one sense only: the Enlightenment worldview, and the Enlightenment philosphers (including, but not limited to, the philosophes), require sustained thinking, not simply faith. The beauty of religion is that faith offers a way of accepting the complexity and contradictions of life. To a large degree, the Enlightenment undermined faith (especially if one reads the Enlightment only casually or reads only their epigoni trying to interpret them) for those who are not constitutionally disposed to think seriously about hard things. While this sort of thing works for those who are serious about philosophical inquiry, that might be .001% of the population. Many writers about the Enlightenment have even tried to define the Enlightenment's substitute faiths, to no satisfaction. Hence, the baleful effects. But, of course, socialism and Marxism provided the replacement for faith in their embrace of dialectcial historical materialism (the great god Diahistomat). Hence the fundamental hostility of Marxism to the Enlightenment even as it sought to build on it.
The author writes: There is that great optimism in human nature, the belief in rationality and science, the conviction that everything has an explanation and that every problem has a solution.
I tried to avoid the language of "faith" in describing the Enlightenment flaw as it seems to be a hackneyed accusation to yell "they worship the false God of reason."