I studied the Koran a great deal. I came away from that study with the conviction there have been few religions in the world as deadly to men as that of Muhammad. So far as I can see, it is the principal cause of the decadence so visible today in the Muslim world and, though less absurd than the polytheism of old, its social and political tendencies are in my opinion to be feared, and I therefore regard it as a form of decadence rather than a form of progress in relation to paganism itself.

Letter to Arthur de Gobineau, 22 October 1843, Tocqueville Reader, p. 229