David Hume lived at a time (the mid 1700s) when many intellectuals greatly admired the ancient world. Indeed they were always dreaming up new ways in which the ancients were superior; Hume tells us that one unnamed writer insisted that there were 50 times more people in the Roman Empire than in the Europe of 1750.
But Hume, one of history's most famous skeptics, wasn't having it. He dismissed that demographic argument as absurd and blasted the ancient world for the violence of its civil wars, and for the prevalence of slavery:
The chief difference between the domestic œconomy of the ancients and that of the moderns consists in the practice of slavery, which prevailed among the former, and which has been abolished for some centuries throughout the greater part of Europe. Some passionate admirers of the ancients, and zealous partizans of civil liberty, (for these sentiments, as they are, both of them, in the main, extremely just, are found to be almost inseparable) cannot forbear regretting the loss of this institution; and whilst they brand all submission to the government of a single person with the harsh denomination of slavery, they would gladly reduce the greater part of mankind to real slavery and subjection. But to one who considers coolly on the subject it will appear, that human nature, in general, really enjoys more liberty at present, in the most arbitrary government of Europe, than it ever did during the most flourishing period of ancient times. As much as submission to a petty prince, whose dominions extend not beyond a single city, is more grievous than obedience to a great monarch; so much is domestic slavery more cruel and oppressive than any civil subjection whatsoever. The more the master is removed from us in place and rank, the greater liberty we enjoy; the less are our actions inspected and controlled; and the fainter that cruel comparison becomes between our own subjection, and the freedom, and even dominion of another. The remains which are found of domestic slavery, in the American colonies, and among some European nations, would never surely create a desire of rendering it more universal. The little humanity, commonly observed in persons, accustomed, from their infancy, to exercise so great authority over their fellow-creatures, and to trample upon human nature, were sufficient alone to disgust us with that unbounded dominion. Nor can a more probable reason be assigned for the severe, I might say, barbarous manners of ancient times, than the practice of domestic slavery; by which every man of rank was rendered a petty tyrant, and educated amidst the flattery, submission, and low debasement of his slaves.
This is worth noting for a couple of reasons. While hypocrisy was everywhere in the Revolutionary era, as in all eras, there were enlightenment figures who actually supported rights for all humans. People like Hume, Benjamin Franklin, Tom Paine, and the Marquis de Condorcet really meant it when they said human rights. They spoke out strongly against slavery and racism. They may not have understood what equality for women would mean or how it would be achieved, but they certainly did not dismiss the notion and most of them supported education for girls. Second, the habit of undermining old heroes by pointing out that they did not live up to modern standards of morality is old, and has been part of many political debates.