In fighting disease, aggressive action is not always advisable. Two years ago a federal panel recommended against routine use of a test for prostate cancer because it carries "a very small potential benefit and significant potential harms." Some men get false positives, and many true positives lead to risky surgery for cancers that grow so slowly as to pose no threat.
Then there is power morcellation, which uses a device to shred uterine fibroids. The Food and Drug Administration has warned against its use in hysterectomies because "there is a risk that the procedure will spread the cancerous tissue within the abdomen and pelvis, significantly worsening the patient's likelihood of long-term survival."
All this has relevance beyond medicine. When President Barack Obama denounced the jihadist group the Islamic State that beheaded American journalist James Foley, he called for action "to extract this cancer so that it does not spread." The United States has been bombing its positions in Iraq and may expand the attacks into Syria. This could be the prelude to a bigger U.S. undertaking.
As least that's what our leaders seem to be hinting at. Defense Secretary Chuck Hagel claimed the Islamic State is a threat "beyond anything that we've seen." Joint Chiefs of Staff Chairman Gen. Martin Dempsey called it an "apocalyptic" group that will "have to be defeated."
The hysteria confirms that the U.S. government can turn any enemy into a rampaging Godzilla posing an imminent threat to our survival. In reality, this one is a fringe insurgency with maybe 10,000 fighters who are stretched thin and outgunned by the Iraqi military.
The group, whose fanatical nature is not in dispute, has managed to rout units of the Iraqi army and gain control of a slice of territory. Its leaders claim to have founded a strict theocratic state on behalf of Muslims the world over. They vow to "raise the flag of Allah in the White House."
If big talk were music, these guys would be a marching band. But issuing threats is easier than making good on them, and seizing turf is not the same as keeping it. The Islamic State's success promises to be its undoing. U.S. military intervention is more likely to multiply the danger than reduce it.
Even Dempsey admits there is no evidence the group is plotting attacks on the U.S. That's not surprising. It's pretty occupied right now fighting the Kurdish army and the Syrian army. Being Sunni in a Shiite-majority country, it isn't likely to try to march to Baghdad, where the Iraqi army would have the help of Shiite militias.
We are supposed to be impressed that the Islamic State controls a swath of land, which al-Qaida never did. But Ohio State University political scientist John Mueller says that's not the advantage it appears to be.
"The fact that they want to hold territory and are likely to deeply alienate the people in their territory means that, unlike terrorists, they will present lucrative targets while surrounded by people who are more than willing to help with intelligence about their whereabouts," he told me.
It's often forgotten that al-Qaida proclaimed its own state in Iraq in 2007, but its brutal ways alienated fellow Sunni insurgent groups so completely that they switched to our side. The Islamic State is equally vulnerable to a backlash.
As for the prospect that it could hit the homeland, our usual problem in deterring terrorists is that their bombs have no return address. The Islamic State, by contrast, is adorned with a neon bull's-eye.
"The place would be a miserable, ostracized blotch on the map with no ability to project power at a distance," argues Paul Pillar of the Center for Security Studies at Georgetown University in The National Interest. It is surrounded by enemies -- not only the Kurds, but the governments of Iraq, Iran and Syria.
Given all the local trouble it faces, the Islamic State can ill afford to focus on attacking the U.S. unless the U.S. focuses on attacking it. Like power morcellation, American military intervention may spread the cancer instead of killing it.
That's been the story of our involvement in wars in that part of the world since 9/11. The more we do the more turmoil there is and the more endangered we feel. But with potential foreign dangers, as with prostate cancer, reflexive fear can be deadly. Sometimes, the safest policy is watchful waiting.