Granted, the reason for the nastiness isn’t hard to understand. Extremist Muslims have led to fear and repugnance toward Islam as a whole. Threats by Muslim crazies just in the last few days forced a Seattle cartoonist, Molly Norris, to go into hiding after she drew a cartoon about Muhammad that went viral.

And then there’s 9/11. When I recently compared today’s prejudice toward Muslims to the historical bigotry toward Catholics, Mormons, Jews and Asian-Americans, many readers protested that it was a false parallel. As one, Carla, put it on my blog: “Catholics and Jews did not come here and kill thousands of people.”

That’s true, but Japanese did attack Pearl Harbor and in the end killed far more Americans than Al Qaeda ever did. Consumed by our fears, we lumped together anyone of Japanese ancestry and rounded them up in internment camps. The threat was real, but so were the hysteria and the overreaction.

Radicals tend to empower radicals, creating a gulf of mutual misunderstanding and anger. Many Americans believe that Osama bin Laden is representative of Muslims, and many Afghans believe that the Rev. Terry Jones (who talked about burning Korans) is representative of Christians.

Many Americans honestly believe that Muslims are prone to violence, but humans are too complicated and diverse to lump into groups that we form invidious conclusions about. We’ve mostly learned that about blacks, Jews and other groups that suffered historic discrimination, but it’s still O.K. to make sweeping statements about “Muslims” as an undifferentiated mass.

In my travels, I’ve seen some of the worst of Islam: theocratic mullahs oppressing people in Iran; girls kept out of school in Afghanistan in the name of religion; girls subjected to genital mutilation in Africa in the name of Islam; warlords in Yemen and Sudan who wield AK-47s and claim to be doing God’s bidding.

But I’ve also seen the exact opposite: Muslim aid workers in Afghanistan who risk their lives to educate girls; a Pakistani imam who shelters rape victims; Muslim leaders who campaign against female genital mutilation and note that it is not really an Islamic practice; Pakistani Muslims who stand up for oppressed Christians and Hindus; and above all, the innumerable Muslim aid workers in Congo, Darfur, Bangladesh and so many other parts of the world who are inspired by the Koran to risk their lives to help others. Those Muslims have helped keep me alive, and they set a standard of compassion, peacefulness and altruism that we should all emulate.

I’m sickened when I hear such gentle souls lumped in with Qaeda terrorists, and when I hear the faith they hold sacred excoriated and mocked. To them and to others smeared, I apologize.