Voltaire. The Philosophical Dictionary. Good read.

What can be said in answer to a man who says he will rather obey God than men, and who consequently feels certain of meriting heaven by cutting your throat? When once fanaticism has gangrened the brain of any man the disease may be regarded as nearly incurable. I have seen Convulsionaries who, while speaking of the miracles of St. Paris, gradually worked themselves up to higher and more vehement degrees of agitation till their eyes became inflamed, their whole frames shook, their countenances became distorted by rage, and had any man contradicted them he would inevitably have been murdered.

Sound familiar at all?

There is no other remedy for this epidemical malady than that spirit of philosophy, which, extending itself from one to another, at length civilizes and softens the manners of men and prevents the access of the disease. For when the disorder has made any progress, we should, without loss of time, fly from the seat of it, and wait till the air has become purified from contagion. Law and religion are not completely efficient against the spiritual pestilence. Religion, indeed, so far from affording proper nutriment to the minds of patients laboring under this infectious and infernal distemper, is converted, by the diseased process of their minds, into poison. These malignant devotees have incessantly before their eyes the example of Ehud, who assassinated the king of Eglon; of Judith, who cut off the head of Holofernes while in bed with him; of Samuel, hewing in pieces King Agag; of Jehoiada the priest, who murdered his queen at the horse-gate. They do not perceive that these instances, which are respectable in antiquity, are in the present day abominable. They derive their fury from religion, decidedly as religion condemns it.

The ‘respectable in antiquity’ thing is irony. Very Gibbonesque – which is to say, Gibbon’s irony was very Voltairean. Gibbon is a good read too.