"A History of Freedom of Thought" by J.B. Bury

Here's a very brief biography of J.B Bury from the Encylopedia Britannica:

Bury, John Bagnell (1861‑1927), British historian, was born on the 16th of October 1861, and was educated at Trinity College, Dublin, where he was elected to a fellowship in 1885. A fine Greek scholar, he edited Pindar's Nemean and Isthmian Odes; but he devoted himself chiefly to the study of history, and was chosen professor of modern history at Dublin in 1893, becoming regius professor of Greek in 1898. He resigned both positions in 1902, when he was elected regius professor of modern history in the university of Cambridge. His historical work was mainly concerned with the later Roman empire, and his edition of Gibbon's Decline and Fall, with a masterly introduction and valuable notes (1896‑1900), is the standard text of this history. He also wrote a History of Greece to the Death of Alexander the Great (1900); History of the Later Roman Empire, 395‑800 (1889), History of the Roman Empire 27 B.C.-180 A.D. (1893); Life of St Patrick and his Place in History (1905), &c. He was elected a fellow of King's College, Cambridge, and received honorary degrees from the universities of Oxford, Edinburgh, Glasgow, Aberdeen and Durham.

And now here are some excerpts from J.B. Bury's A History of Freedom of Thought, specifically from Chapter II Reason Free, Greece and Rome. The book was first published in 1913, and the whole thing is available for free download via Project Gutenberg. All emphases have been added.

The outcome of the large freedom permitted at [classical] Athens was a series of philosophies which had a common source in the conversations of Socrates. Plato, Aristotle, the Stoics, the Epicureans, the Sceptics—it may be maintained that the efforts of thought represented by these names have had a deeper influence on the progress of man than any other continuous intellectual movement, at least until the rise of modern science in a new epoch of liberty.

The doctrines of the Epicureans, Stoics, and Sceptics all aimed at securing peace and guidance for the individual soul. They were widely propagated throughout the Greek world from the third century B.C., and we may say that from this time onward most well-educated Greeks were more or less rationalists. The teaching of Epicurus had a distinct anti-religious tendency. He considered fear to be the fundamental motive of religion, and to free men’s minds from this fear was a principal object of his teaching. He was a Materialist, explaining the world by the atomic theory of Democritus and denying any divine government of the universe. He did indeed hold the existence of gods, but, so far as men are concerned, his gods are as if they were not—living in some remote abode and enjoying a “sacred and everlasting calm.” They just served as an example of the realization of the ideal Epicurean life.

There was something in this philosophy which had the power to inspire a poet of singular genius to expound it in verse. The Roman Lucretius (first century B.C.) regarded Epicurus as the great deliverer of the human race and determined to proclaim the glad tidings of his philosophy in a poem On the Nature of the World. With all the fervour of a religious enthusiast he denounces religion, sounding every note of defiance, loathing, and contempt, and branding in burning words the crimes to which it had urged man on. He rides forth as a leader of the hosts of atheism against the walls of heaven. He explains the scientific arguments as if they were the radiant revelation of a new world; and the rapture of his enthusiasm is a strange accompaniment of a doctrine which aimed at perfect calm. Although the Greek thinkers had done all the work and the Latin poem is a hymn of triumph over prostrate deities, yet in the literature of free thought it must always hold an eminent place by the sincerity of its audacious, defiant spirit. In the history of rationalism its interest would be greater if it had exploded in the midst of an orthodox community. But the educated Romans in the days of Lucretius were sceptical in religious matters, some of them were Epicureans, and we may suspect that not many of those who read it were shocked or influenced by the audacities of the champion of irreligion.

The Stoic philosophy made notable contributions to the cause of liberty and could hardly have flourished in an atmosphere where discussion was not free. It asserted the rights of individuals against public authority. Socrates had seen that laws may be unjust and that peoples may go wrong, but he had found no principle for the guidance of society. The Stoics discovered it in the law of nature, prior and superior to all the customs and written laws of peoples, and this doctrine, spreading outside Stoic circles, caught hold of the Roman world and affected Roman legislation.

These philosophies have carried us from Greece to Rome. In the later Roman Republic and the early Empire, no restrictions were imposed on opinion, and these philosophies, which made the individual the first consideration, spread widely. Most of the leading men were unbelievers in the official religion of the State, but they considered it valuable for the purpose of keeping the uneducated populace in order. A Greek historian expresses high approval of the Roman policy of cultivating superstition for the benefit of the masses. This was the attitude of Cicero, and the view that a false religion is indispensable as a social machine was general among ancient unbelievers. It is common, in one form or another, to-day; at least, religions are constantly defended on the ground not of truth but of utility. This defence belongs to the statecraft of Machiavelli, who taught that religion is necessary for government, and that it may be the duty of a ruler to support a religion which he believes to be false.

A word must be said of Lucian (second century A.D.), the last Greek man of letters whose writings appeal to everybody. He attacked the popular mythology with open ridicule. It is impossible to say whether his satires had any effect at the time beyond affording enjoyment to educated infidels who read them. Zeus in a Tragedy Part is one of the most effective. The situation which Lucian imagined here would be paralleled if a modern writer were blasphemously to represent the Persons of the Trinity with some eminent angels and saints discussing in a celestial smoke-room the alarming growth of unbelief in England and then by means of a telephonic apparatus overhearing a dispute between a freethinker and a parson on a public platform in London. The absurdities of anthropomorphism have never been the subject of more brilliant jesting than in Lucian’s satires.....
[pp. 37-40]

The relations between the Roman government and the Christians raised the general question of persecution and freedom of conscience. A State, with an official religion, but perfectly tolerant of all creeds and cults, finds that a society had arisen in its midst which is uncompromisingly hostile to all creeds but its own and which, if it had the power, would suppress all but its own. The government, in self-defence, decides to check the dissemination of these subversive ideas and makes the profession of that creed a crime, not on account of its particular tenets, but on account of the social consequences of those tenets. The members of the society cannot without violating their consciences and incurring damnation abandon their exclusive doctrine. The principle of freedom of conscience is asserted as superior to all obligations to the State, and the State, confronted by this new claim, is unable to admit it. Persecution is the result.

Even from the standpoint of an orthodox and loyal pagan the persecution of the Christians is indefensible, because blood was shed uselessly. In other words, it was a great mistake because it was unsuccessful. For persecution is a choice between two evils. The alternatives are violence (which no reasonable defender of persecution would deny to be an evil in itself) and the spread of dangerous opinions. The first is chosen simply to avoid the second, on the ground that the second is the greater evil. But if the persecution is not so devised and carried out as to accomplish its end, then you have two evils instead of one, and nothing can justify this. From their point of view, the Emperors had good reasons for regarding Christianity as dangerous and anti-social, but they should either have let it alone or taken systematic measures to destroy it. If at an early stage they had established a drastic and systematic inquisition, they might possibly have exterminated it. This at least would have been statesmanlike. But they had no conception of extreme measures, and they did not understand —they had no experience to guide them —the sort of problem they had to deal with. They hoped to succeed by intimidation. Their attempts at suppression were vacillating, fitful, and ridiculously ineffectual. The later persecutions (of A.D. 250 and 303) had no prospect of success. It is particularly to be observed that no effort was made to suppress Christian literature.

The higher problem whether persecution, even if it attains the desired end, is justifiable, was not considered. The struggle hinged on antagonism between the conscience of the individual and the authority and supposed interests of the State. It was the question which had been raised by Socrates, raised now on a wider platform in a more pressing and formidable shape: what is to happen when obedience to the law is inconsistent with obedience to an invisible master? Is it incumbent on the State to respect the conscience of the individual at all costs, or within what limits? The Christians did not attempt a solution, the general problem did not interest them. They claimed the right of freedom exclusively for themselves from a non-Christian government; and it is hardly going too far to suspect that they would have applauded the government if it had suppressed the Gnostic sects whom they hated and calumniated. In any case, when a Christian State was established, they would completely forget the principle which they had invoked. The martyrs died for conscience, but not for liberty. To-day the greatest of the Churches demands freedom of conscience in the modern States which she does not control, but refuses to admit that, where she had the power, it would be incumbent on her to concede it.

If we review the history of classical antiquity as a whole, we may almost say that freedom of thought was like the air men breathed. It was taken for granted and nobody thought about it. If seven or eight thinkers at Athens were penalized for heterodoxy, in some and perhaps in most of these cases heterodoxy was only a pretext. They do not invalidate the general facts that the advance of knowledge was not impeded by prejudice, or science retarded by the weight of unscientific authority. The educated Greeks were tolerant because they were friends of reason and did not set up any authority to overrule reason. Opinions were not imposed except by argument; you were not expected to receive some “kingdom of heaven” like a little child, or to prostrate your intellect before an authority claiming to be infallible.

But this liberty was not the result of a conscious policy or deliberate conviction, and therefore it was precarious. The problems of freedom of thought, religious liberty, toleration, had not been forced upon society and were never seriously considered. When Christianity confronted the Roman government, no one saw that in the treatment of a small, obscure, and, to pagan thinkers, uninteresting or repugnant sect, a principle of the deepest social importance was involved. A long experience of the theory and practice of persecution was required to base securely the theory of freedom of thought. The lurid policy of coercion which the Christian Church adopted, and its consequences, would at last compel reason to wrestle with the problem and discover the justification of intellectual liberty. The spirit of the Greeks and Romans, alive in their works, would, after a long period of obscuration, again enlighten the world and aid in re-establishing the reign of reason, which they had carelessly enjoyed without assuring its foundations.
[pp. 48-51]