Friday’s admission by the Biden administration that an August drone strike in Kabul accidentally killed an Afghan aid worker and his children demonstrated the limits of “over the horizon” counterterror operations. Such strikes can either scrupulously avoid Afghan civilian casualties or effectively protect American civilians—not both. Policy makers who think otherwise are misinformed.

In the second half of the 20th century, most U.S. presidents and civilian national security officials had spent time in uniform. They had a sense...

The site of the U.S. airstrike in Kabul, Afghanistan, Sept. 3.

Photo: Saifurahman Safi/Zuma Press

Friday’s admission by the Biden administration that an August drone strike in Kabul accidentally killed an Afghan aid worker and his children demonstrated the limits of “over the horizon” counterterror operations. Such strikes can either scrupulously avoid Afghan civilian casualties or effectively protect American civilians—not both. Policy makers who think otherwise are misinformed.

In the second half of the 20th century, most U.S. presidents and civilian national security officials had spent time in uniform. They had a sense of what the military can and can’t do. Some actually had fingertip feel of what happens when America goes to war. Since 9/11, however, combat veterans have been conspicuously underrepresented among senior Washington policy makers. The Biden administration seems especially underresourced when it comes to battlefield experience.

Popular culture advances an illusion that military leaders receive accurate, timely and granular intelligence at a keystroke via modern technology. After debate and cool reflection, wise generals reluctantly order a drone from thousands of miles away to kill only the identified target. The reality is dirtier. Exhausted field-grade officers operate on incomplete information of varying quality, freshness and detail. Low fuel and bad weather will put time limitations on the airborne assets at the disposal of decision makers. This stress often forces a lonely choice to launch a strike that, despite best efforts, may cause civilian deaths.

Until recently, these difficult choices were supported by human intelligence on the ground in Afghanistan. Spies could collect actionable information. Detainees could be interrogated. Computers, phones and “pocket litter” seized on raids could be exploited for targeting purposes. Close-target reconnaissance and tactical-imagery and signals intelligence could identify targets’ faces, vehicles and voices, and geolocate them. Having aircraft in the country meant fewer tough trade-offs. Pilots could burn less fuel, giving them longer range and loiter times. They could wait for a target to move so that a missile strike wouldn’t endanger others. These overlapping capabilities often provided the “surgical” results that policy makers and the public crave. They’re all gone now.

Remember what actionable intelligence to prevent 9/11 would have looked like. U.S. agencies would have needed knowledge of al Qaeda’s intent to fly airliners into American buildings, the intended hijackers’ identities and their current or prospective locations, and legally admissible evidence to imprison them in Malaysia, Germany or the U.S. You can’t get all that from a digital camera on a drone. With no U.S. presence in Afghanistan, the administrations of Presidents Bill Clinton and George W. Bush couldn’t obtain that information. What makes the Biden administration think it can do so now?

Al Qaeda is a terrorist organization. Its secrets can’t be learned by recruiting sources on the diplomatic cocktail circuit as spies, nor by commercial espionage. Technology-dependent covert actions are of limited use. There’s nowhere to hide a beacon on a boxcutter.

Without the benefit of ground truth in Afghanistan, we’re left with the blunt instrument of airpower to prevent another 9/11. It is no criticism of the skill or bravery of our airmen and aviators to point out that airstrikes, even using precision-guided munitions, involve high explosives moving at hundreds of miles an hour. Accidents happen and innocents get killed. The American people, for better or worse, no longer have any appetite for such civilian casualties.

So we are left to wait for the inevitable: another attack. Mr. Biden and his team should be more forthright about the stark choice he has made.

Mr. Carroll served as senior counselor to Homeland Security Secretary John F. Kelly, 2017-18, and as an Army and Central Intelligence Agency officer in Afghanistan, Iraq and Yemen.

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