WASHINGTON — There's a difference between sensitivity and stupidity. If there were indeed signs that Maj. Nidal Hasan, the alleged Fort Hood mass murderer, was becoming radicalized in his opposition to the U.S. wars in Iraq and Afghanistan, the Army had a duty to act — before he did.

Gen. George Casey, the Army chief of staff, said Sunday he was concerned that "this increased speculation" about Hasan's evolving political and religious views "could cause a backlash against some of our Muslim soldiers." Casey is right to worry about the lunatics and bigots who now will think of all Muslims in the military as potential enemies. But it only feeds such paranoia to ignore alarm bells that an unstable individual, Muslim or not, is about to blow.

According to published reports, Hasan told people of his serious doubts about the U.S. military campaigns in Iraq and Afghanistan. Hasan, a psychiatrist who had evaluated returning soldiers for stress-related disorders, made no secret of his reluctance to serve in the Afghan theater, where he was to be sent within weeks. According to ABC News, fellow Army doctors told superiors of their concern that Hasan felt divided allegiance — both to the Muslims whom he felt were under attack and the country he had volunteered to serve.

All this should have been enough to prompt an urgent intervention by Army brass, regardless of Hasan's religion. That it did not is unfair to the thousands of Muslims who have served in the military, and continue to do so, with honor and distinction.

"The system is not doing what it's supposed to do," Army doctor Val Finnell told The Associated Press. Finnell, who studied with Hasan, complained to higher-ups about Hasan's "anti-American" rants and his stated view that the United States was conducting a war against Islam. "He at least should have been confronted about these beliefs, told to cease and desist, and to shape up or ship out."

Indeed he should have been. In the Army, there's a rich tradition of grousing about idiotic higher-ups and their ridiculous orders. But it sounds as if Hasan's complaints went far beyond the ordinary, especially in the notion that he might be unsure of his own loyalty and duty.

If Hasan's superior officers had investigated, they might have pieced together the story that seems to be emerging: that Hasan was behaving erratically, that his faith apparently had become increasingly political, that he desperately wanted out of the military and that he was distraught about being ordered to the war zone.

Army officials surely were aware that Muslims in the service have complained of taunts and harassment from their fellow soldiers. For both moral and practical reasons, the Army must eliminate such discrimination. I've had issues with the way former President George W. Bush did his job, to say the least, but one good thing he did was emphasize that his "war on terrorism" was not a war against Islam, one of the world's great faiths. That disclaimer rings hollow if Muslims serving in the armed forces are blamed for the crimes of Islamic terrorists and treated as potential traitors to the American cause.

But fairness is one thing, foolishness is another. Any soldier who seemed as if he might be falling apart — and it seems that Hasan gave a lot of people that impression — should have been given extra scrutiny. In Hasan's case, a closer look would have revealed his growing religiosity and his feeling that his faith was under assault.

The fact that Hasan had worshiped at a Virginia mosque whose spiritual leader was a radical named Anwar al-Aulaqi might also have come to light. The Washington Post reported Monday that Aulaqi, who now lives in Yemen, has posted a message on his Web site calling Hasan a "hero" for what he allegedly did at Fort Hood.

Had authorities learned in advance of any link between Hasan and radical Islam — as opposed to the mainstream Islam practiced by more than a billion people worldwide — they could have moved immediately to ensure that Hasan could not hurt others or himself. That wouldn't have been an act of bigotry, it would have been an act of prudence, even compassion.

How is the Pentagon supposed to tell the difference between reasonable caution and blatant discrimination? There are thousands of Muslims in uniform, serving their country at home and abroad. Ask them.

Eugene Robinson's e-mail address is eugenerobinson@washpost.com.