“Opinions upon moral questions are more often the expression of strongly felt expediency than of careful ethical reasoning; and the opinions so formed by one generation become the conscientious convictions or the sacred instincts of the next.”

Französische Bühne (The French Stage), ch. 9 (1837)
Original: (de) Die Menschen in jener alten Zeit hatten Überzeugungen, wir Neueren haben nur Meinungen, und es gehört etwas mehr als eine bloße Meinung dazu, um so einen gotischen Dom aufzurichten.

A Bill for Establishing Religious Freedom, Chapter 82 (1779). Published in The Works of Thomas Jefferson in Twelve Volumes http://oll.libertyfund.org/ToC/0054.php, Federal Edition, Paul Leicester Ford, ed., New York: G. P. Putnam's Sons, 1904, Vol. 1 http://oll.libertyfund.org/Texts/Jefferson0136/Works/0054-01_Bk.pdf, pp. 438–441. Comparison of Jefferson's proposed draft and the bill enacted http://web.archive.org/web/19990128135214/http://www.geocities.com/Athens/7842/bill-act.htm
1770s
Variant: Our civil rights have no dependence on our religious opinions any more than our opinions in physics or geometry...
Source: The Statute Of Virginia For Religious Freedom
Context: Well aware that the opinions and belief of men depend not on their own will, but follow involuntarily the evidence proposed to their minds; that Almighty God hath created the mind free, and manifested his supreme will that free it shall remain by making it altogether insusceptible of restraint; that all attempts to influence it by temporal punishments, or burthens, or by civil incapacitations, tend only to beget habits of hypocrisy and meanness, and are a departure from the plan of the holy author of our religion, who being lord both of body and mind, yet choose not to propagate it by coercions on either, as was in his Almighty power to do, but to exalt it by its influence on reason alone; that the impious presumption of legislature and ruler, civil as well as ecclesiastical, who, being themselves but fallible and uninspired men, have assumed dominion over the faith of others, setting up their own opinions and modes of thinking as the only true and infallible, and as such endeavoring to impose them on others, hath established and maintained false religions over the greatest part of the world and through all time: That to compel a man to furnish contributions of money for the propagation of opinions which he disbelieves and abhors, is sinful and tyrannical; … that our civil rights have no dependence on our religious opinions, any more than our opinions in physics or geometry; and therefore the proscribing any citizen as unworthy the public confidence by laying upon him an incapacity of being called to offices of trust or emolument, unless he profess or renounce this or that religions opinion, is depriving him injudiciously of those privileges and advantages to which, in common with his fellow-citizens, he has a natural right; that it tends also to corrupt the principles of that very religion it is meant to encourage, by bribing with a monopoly of worldly honours and emolumerits, those who will externally profess and conform to it; that though indeed these are criminals who do not withstand such temptation, yet neither are those innocent who lay the bait in their way; that the opinions of men are not the object of civil government, nor under its jurisdiction; that to suffer the civil magistrate to intrude his powers into the field of opinion and to restrain the profession or propagation of principles on supposition of their ill tendency is a dangerous fallacy, which at once destroys all religious liberty, … and finally, that truth is great and will prevail if left to herself; that she is the proper and sufficient antagonist to error, and has nothing to fear from the conflict unless by human interposition disarmed of her natural weapons, free argument and debate; errors ceasing to be dangerous when it is permitted freely to contradict them.

Es ist nicht der Kampf der Meinungen, welcher die Geschichte so gewaltthätig gemacht hat, sondern der Kampf des Glaubens an die Meinungen, das heisst der Ueberzeugungen.
Section IX, "Man Alone with Himself" / excerpt from aphorism 630
Source: Human, All Too Human (1878), Helen Zimmern translation

Source: Sustainable History and the Dignity of Man (2009), p.437

1850s, The Present Aspect of the Slavery Question (1859)
Context: And as I understand the Republican party, while it steadily holds that slavery is in itself a wrong, it does not forget human conditions and the actual state of things, and, therefore, that the questions of planting slavery in fresh territory and of removing it where it is in wrought in a system of society are very different, as different as the prevention and the cure of disease. The question of the moment, then, is simply whether the most unrelenting and permanent despotism can be justified by the Constitution of the United States. That is, whether the makers of the government meant that the democratic-republican principle should gradually, but surely, disappear from that government. There are, therefore, but two parties, one holding that a system of free society, the other that one of slave society, is the real intention of the government. These parties are sectionally divided in situation, but they both aim to have their idea become the national policy. The party of slavery, indeed, is divided in its own camp, but only upon a minor question. The point of difference between Mr. Douglas and Mr. Buchanan is not whether all men under this government have rights, but simply in what way those who deprive them of those rights shall be most securely protected. Mr. Douglas argues that the slave party is the only national party; 'because', he says, 'so long as we live under a common Constitution, any political creed which cannot be proclaimed wherever that Constitution is the supreme law of the land must be ruinous and fatal'. He makes short work of it For it is a matter of fact that the creed of equal human and consequent political rights cannot be proclaimed everywhere in the country; and therefore whoever, in the present juncture of our affairs, can proclaim his entire political creed as frankly in Charleston as in Boston, can do it only because he has stricken from the list our distinctive national principle, without which we are not Americans at all — the natural equal rights of men. If Washington or Jefferson or Madison should utter upon his native soil today the opinions he entertained and expressed upon this question, he would be denounced as a fanatical abolitionist. To declare the right of all men to liberty is sectional, because slavery is afraid of liberty and strikes the mouth that speaks the word. To preach slavery is not sectional — no: because freedom respects itself and believes in itself enough to give an enemy fair play. Thus Boston asked Senator Toombs to come and say what he could for slavery. I think Boston did a good thing, but I think Senator Toombs is not a wise man, for he went. He went all the way from Georgia to show Massachusetts how slavery looks, and to let it learn what it has to say. When will Georgia ask Wendell Phillips or Charles Sumner to come down and show her how liberty looks and speaks?

Youtube, Other, The Damn Commandments https://www.youtube.com/watch?v=8u3z69YpLx0 (January 7, 2015)

Source: The Subjection of Women

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 440.

Original: In amore, se fosse utile esprimere la propria opinione, non ce lo lascerebbero fare.
Source: prevale.net