In their encyclicals from 1789 until Vatican II, the popes frequently insinuate that the object of the Enlightenment wasn't to increase human liberty, but to destroy Christian civilization. To modern ears, they can seem grumpy and intemperate (think of Leo XIII's Syllabus of Errors), filled with passionate denunciations instead of calm refutations. For this reason, they were often dismissed as hopeless reactionaries.
It would be wrong to wholly dismiss the entire project of the Enlightenment -- and indeed, the encyclicals do no such thing, identifying positive developments while they condemn errors and half-truths. Men of the Enlightenment improved man's earthly life by emphasizing natural rights and forcing governments to recognize them. This is particularly true in the Anglo-American strain, much less so in the French, which begot mass bloodletting, vicious and supremely arrogant colonialism, and violent repression of the Church.
Common to all Enlightenment schools of thought was the belief in the right to free speech. At its noblest, this was a recognition that no human institution could long survive without honest criticism, protected from reprisals such as arrest or confiscation of property.
For most of the modern era, this belief has been loudly proclaimed by all of those who claim the Enlightenment as their intellectual lineage, most particularly by those who call themselves "liberals." These classical liberals had an honorable record of defending the rights of the despised, particularly those who wanted to advance an unpopular view against powerful interests.
But those kinds of liberals were eclipsed in the 1960s by the New Left, which saw classical liberals as the enemy. In the New Left's view, Western society was irredeemably corrupt, as it bore evil fruits such as colonialism and racism. Liberals, they thought, were much more dangerous to "progress" because they gave a veneer of legitimacy for Western values, most prominently Christianity, and thus they had to be destroyed.
After some initial resistance, the New Left triumphed in a rout. They now lead the left-leaning political parties in every Western nation. In the academy and the arts, they enjoy near-total dominance; whole communions of Protestant churches were given over to them. Thus, most of the people we call "liberals" today aren't really liberals, they are the New Leftists and their progeny. They continue to belive that Western society must be undermined, but now they wield real power and influence.
The reason they are still called "liberals" is because the New Left retained traditional liberal rhetoric to advance its agenda. They continued to support free speech -- as long as there was no cost. Thus, in the late 1970s, the ACLU defended the right of Nazis to march in the predominantly Jewish town of Skokie, Illinois. The ACLU's supporters have flaunted this support for decades as proof of their "free speech" principles.
But there was never any danger of the Nazis taking over Skokie, or anyplace else. It didn't threaten any New Left power center, either, so they were risking exactly nothing. Similarly, when the government of Iran condemned Salman Rushdie to death for the "blasphemy" in his novel The Satanic Verses, Western liberals practically tripped over themselves in their haste to show their solidarity with Rushdie. They bought his book, staging public readings, and writing self-righteous essays about the dangers of censorship and the glories of artistic freedom.
Today, the same voices are mostly silent. Defending a man with a scimitar at his neck was easy when his would-be executioners were unlikely to attack. In 1988, Iran operated a highly effective regional terrorist network through Hezbollah, but it had no global reach, and the Islamic Republic was recovering from an eight-year war with its neighbor Iraq. The potential that it could carry out its threat was slim.
This hypocrisy and cowardice of the Left is currently on display in the Danish cartoon controversy Muhammad. Whenever an "artist" drops elephant poo-poo on a picture of Our Lady, or writes a play showing Our Lord as a practicing homosexual, you can count on modern liberals to start bleating "free speech, free speech." But when Muslims riot, burn, and kill because they don't like some disrespectful drawings, liberals suddenly fall silent.
Now, Islamofascist jihad is a worldwide phenomenon, not confined to a single Middle Eastern nation. Freelance jihadi scumbags have murdered their opponents in Europe and the U.S., and these attacks show no signs of ceasing. Supporting a free-speech cause celebre isn't a risk-free proposition anymore.
Cowardice is only part of the explanation for the Left's silence. They also believe that the Darker Peoples are less than fully human, and can't be fully blamed for any of their actions. This crude racialism permeates and corrupts their moral sense on most social issues. Foremost, and most shamefully, many Leftists sympathize with the Islamofacists' goal of destroying the West.
The two groups don't agree with each other on every issue -- the Western Left practically regards gay sex as a sacrament, and Islamofacists wouldn't mind stoning gays to death. The latter group's views on "the status of women" are notoriously retrograde. In their fundamental view of Western civilization, though, their critiques are roughly the same: it is dangerously corrupt, exercises a malign influence in the world, and its power should be thwarted at every opportunity.
So the popes were right after all. The children of the Enlightenment do not even mouth the words of their own creed anymore when they are confronted by murderous thugs. They urge "restraint" to appease Muslim mobs, and shout down Christians who object to their own faith being lampooned or insulted. The Left has, in effect, chosen its side in the clash of civilizations, and they are de facto on the side of the Islamofascists.
The politics of appeasement - I see the ghost of Neville Chamberlin riding forth.....