Religious indifferentism.
The Enlightenment taught us to ignore religious differences. We were taught in school that the Enlightenment was good. But aside from Smith and Locke, the philosophers represent a rogues gallery:
a European intellectual movement of the late 17th and 18th centuries emphasizing reason and individualism rather than tradition. It was heavily influenced by 17th-century philosophers such as Descartes, Locke, and Newton, and its prominent exponents include Kant, Goethe, Voltaire, Rousseau, and Adam Smith.
As a high schooler, when studying the First Amendment, I remember wondering, Can a a country that tolerates all religions tolerate a religion that doesn't tolerate other religions? At the time, I was thinking of satanism. The question certainly applies to Islam.
It turns out that Jefferson didn't understand the nature of Islam, either. During the US conflict with the Barbary pirates, Jefferson sent a delegate to North Africa to speak to the caliph. The ambassador asked, "Why do you steal from us? We have no quarrel with you." The caliph said, "you are infidels. We can take what we like from you."
Jefferson was shocked and decided to read the Koran for himself.
Belated thanks for your thoughtful and educated response. :)