The author of a controversial book called "The End of Faith" says an unspoken rule against criticizing religion needs to be re-thought in an age of religious terrorism. Author Sam Harris says people of all faiths need to be respected, but religious beliefs should not be sacrosanct.

Religion, say its adherents, has the power to inspire, to provide a moral compass and sense of meaning. But its critics say faith also has its dark side. Differences over religion have divided communities and sparked violent conflicts. Partly for that reason, most people today avoid addressing religious differences.

Writer Sam Harris says, however, the spread of new technology, including nuclear weapons that can fit into a suitcase, has created a world where the rule no longer applies.

"It was never the case even 50 years ago that one person, based on his zeal to find his way into paradise, could destroy the lives of millions of people," he said. "And we're fast approaching a time where weapons of mass destruction, weapons of mass disruption, even being able to spread viruses on the Internet, can be so confounding to society that we really have to get our act together in a way that we really didn't even 50 years ago."

The author of The End of Faith takes rhetorical aim at Islamic militants who see themselves engaged in a war against infidels, and at Christian fundamentalists who he says want to impose their moral views on abortion and sexuality on others. He says politics requires a more nuanced discussion than some religious people are willing to engage in.

The problem, in his view, is not just with fundamentalism, but also with moderate religion, which he says contains the seeds of extremism. John Crossley, a professor of religion at the University of Southern California, sees merit in some of Mr. Harris' observations.

"He is clearly morally outraged at the violence that's being done in the world in the name of religion, in the name of faith," he said. "I think, though, that he makes a fundamental category mistake when he attributes the problem not just to religious fanaticism or to certain types of faith, but when he denigrates faith itself and contrasts it with reason."

Mr. Harris is not a conventional atheist, and says atheism often carries a "whiff of formaldehyde," ignoring much of life's authentic mystery. He also rejects suggestions that religion be suppressed as it has been in many communist countries. In fact, he says, communism is a faith-based ideology as much as religion is. He says on questions of faith, he is simply suggesting "new rules of conversation."

"I'm not recommending laws or that we imprison people or anything else, simply that it no longer be taboo to challenge someone's religious beliefs," he said.

The author believes that life indeed has a spiritual dimension, but says it should be accessible to scientific study. As a college undergraduate, he studied philosophy and is now completing a doctorate in neuroscience. He says the world's mystics may offer insights into the human condition, but adds that spirituality should be subject to the same rigorous tests as other forms of knowledge.

Professor Crossley responds that Mr. Harris' conception of faith is much too narrow. Faith, says the professor, is more than a list of dogmas, although he agrees it is sometimes viewed that way.

"I think he's right in many ways because faith, whatever kind of experience it's based on, can very easily become rigidified into a certain set of beliefs or propositions, and then one can act in the name of those propositions," he said. "But what he does is to equate faith in its most fundamental sense with beliefs in these set propositions."

Mr. Crossley says faith, for him, stems from a personal sense of the transcendent.

"And that's based on one's own natural feeling of dependence," he said. "We didn't make ourselves. We don't know where we came from, and we know we're finite and limited and we're going to die. And for a sense of the transcendent to develop in a person seems to be very natural."

Author Sam Harris says religion incorporates valid ethical insights about the need to love one's neighbors, for example, but says non-religious people have the same insights. And he acknowledges the role of religious ritual in bringing people together for important events like births and marriages. But he says communal ceremonies need not be religious.

"I would argue that we need to craft rituals and discourse that is not an offense to all that we have discovered about the world in the last 2,000 years, but which is equally powerful, equally solidifying of community," he said. "And I don't see any reason why we can't do that."

He says people who subscribe to the world's religions have every right to do so, but says they should be open to challenge if they try to impose their views on others.

Professor Crossley responds that religion is not inherently rigid, and that faith, at its best, promotes peace, tolerance and openness.

Sam Harris' book, The End of Faith: Religion, Terror, and the Future of Reason, is published by W. W. Norton.