Charles Mackay said this quote

Men, it has been well said, think in herds; it will be seen that they go mad in herds, while they only recover their senses slowly, one by one.

~ Charles Mackay

In reading The History of Nations, we find that, like individuals, they have their whims and their peculiarities, their seasons of excitement and recklessness, when they care not what they do. We find that whole communities suddenly fix their minds upon one object and go mad in its pursuit; that millions of people become simultaneously impressed with one delusion, and run after it, till their attention is caught by some new folly more captivating than the first.

~ Charles Mackay

Three causes especially have excited the discontent of mankind; and, by impelling us to seek remedies for the irremediable, have bewildered us in a maze of madness and error. These are death, toil, and the ignorance of the future..

~ Charles Mackay

Let us not, in the pride of our superior knowledge, turn with contempt from the follies of our predecessors. The study of the errors into which great minds have fallen in the pursuit of truth can never be uninstructive. As the man looks back to the days of his childhood and his youth, and recalls to his mind the strange notions and false opinions that swayed his actions at the time, that he may wonder at them; so should society, for its edification, look back to the opinions which governed ages that fled.

~ Charles Mackay