Hehir said he believed the terrorism presented a just cause for war as long as the United States limited itself to targeting only the guilty.

“The question is to remember the civilian society that is neither the state nor the terrorists,” he said. “In Afghanistan, it’s the refugees.”

Asked what number of accidental civilian casualties would be acceptable, he said there was no “magic number” but that one should use a “sense of moral judgment.”

“It may be there are targets you have to forgo because it’s highly likely you will kill civilians,” Hehir said.

The panel concluded the discussion by looking at what U.S. responsibilities would be in the aftermath of war with Afghanistan, a consideration which Ignatieff said most American citizens had not yet faced.

“We have an obligation to rebuild, to create a governing structure, and I don’t think that can be discharged unless you have a temporary U.N. administration,” he said.

Hehir said the job might be harder than it looks.

“The moral mandate is there, but I do not want to entrust the world to American knowledge of Afhani politics,” he said.