(RNS) In September 2001, Sam Harris was an unknown doctoral student who didn't believe in God.

But after the World Trade Center crumbled on 9/11, he put his studies aside to write a book that became an instant best-seller -- and changed the way atheists, and perhaps Muslims, are perceived in this country.

Published in 2004, Harris's "The End of Faith" launched the so-called "New Atheist" movement, a make-no-apologies ideology that maintains that religion is not just flawed, but evil, and must be rejected. 

In the book, Harris frequently uses the image of a Muslim suicide bomber to highlight the dangers of religion, depicting Islam as a "cult of death" and a "machinery of intolerance and suicidal grandiosity." Within two years, Harris was joined on the best-seller list by Richard Dawkins, Christopher Hitchens and Daniel Dennett, who all took religion to task for most -- if not all -- of the world's ills.

Collectively, the men whose books sold millions of copies around the world came to be known as the apocalyptic-sounding "Four Horsemen." Now, 10 years after the 9/11 attacks that launched the movement, freethinkers are taking stock of the New Atheists contributions to their community, which includes atheists, agnostics, humanists and other nonreligionists. 

Many laud their defense of what they see as a truthful but unpopular stance. Others, meanwhile, say their heavy-handedness with people of faith -- especially Muslims -- has caused irreparable harm.

"9/11 ushered in a big change, in that it put Islam squarely in the center of the discussion," said Tom Flynn, director of The Center for Inquiry, and a supporter of the New Atheists. "Previous freethinkers would have said religion is horrible, look at the Crusades, look at the Inquisition. This opened up the possibility of directing strong arguments against religions other than Christianity."

Flynn points out that atheists have long called for an end to religion. What's "new" about the New Atheists is their stridency and refusal to compromise. 

"I think religion should be treated with ridicule, hatred and contempt, and I claim that right," Hitchens told a Toronto audience in 2007. Freethinkers who are in dialogue with people of faith are "accommodationists," the New Atheists have charged, and "enemies" of the movement.

That rift has had real consequences. In 2010, Paul Kurtz was ousted as founding leader of the Council for Secular Humanism and the Center for Inquiry in what he described as a "palace coup." Talk amongst the freethinkers was that Kurtz was too accommodationist.

"They're anti-religious, and they're mean-spirited, unfortunately," Kurtz told NPR in 2009. "Now, they're very good atheists and very dedicated people who do not believe in God. But you have this aggressive and militant phase of atheism, and that does more damage than good."

Harris declined to be interviewed for this article, and Dawkins and Dennett could not be reached. Hitchens, who is battling cancer, is too ill to conduct interviews.

But the New Atheists have also done good, observers say. Fred Edwords, head of the United Coalition of Reason, an umbrella group of freethought organizations, describes 2004 (the year Harris's book hit the shelves) as "the year the dam broke."

"My job exists because of all the new local groups that emerged in the wake of the rise of the New Atheists," Edwords said. "And the publicity that I generate for these groups tends to attract people who found their own identity because of the New Atheism."

One such beneficiary is The Freedom From Religion Foundation, which was mentioned in Dawkins' "The God Delusion." In 2004, it had fewer than 6,000 members. By 2007, membership had doubled, and this year topped 17,000.

"We feel like we owe a huge debt to these people," Dan Barker, co-president of the foundation, said of the Four Horsemen, many of whom have appeared at FFRF events.

While multiple factors have affected Americans' negative views of Islam after 9/11, many American Muslims partially blame the New Atheists. A 2010 Pew poll found that only 30 percent of Americans have a favorable view of Islam, down from 41 percent in 2005, a year after Harris' book.

"I would say they have harmed," Omid Safi, a Muslim and a professor of religious studies at the University of North Carolina, Chapel Hill. "They direct much of their venom against Muslims, and I have seen some of their material used by Islamophobes."

Even so, there have been bridges built. The Secular Student Alliance, which blossomed from 59 campus groups when "The God Delusion" appeared to 273 today, is now routinely invited to participate in interfaith projects with Muslim students.

"This is something we would not have seen before the New Atheists made sure we were on everybody's mind," said Jesse Galef, a spokesman for the SSA. "The attention has done wonders."

Ryan Cragun, a sociologist of religion at the University of Tampa, is more qualified in his assessment. In their extremism and intolerance, he likens the New Atheists to Fox News Channel -- "so far to the right," he said, that they opened up the middle.

"Now it is OK to be a moderate atheist because you can point to the stridency of the New Atheists and say, `At least I am not one of them,"' he said. "It opens up a bigger space for freethinkers to actually communicate."