"It would have been offensive and incomprehensible to consciously leave an American behind, no matter what, to leave an American behind in the hands of people who would torture him, cut of his head, do any number of things," Kerry said. "And we would consciously choose to do that? That's the other side of this equation. I don't think anybody would think that's an appropriate thing to do."
Kerry said it was possible that the released detainees would return to terrorist activity.
"I'm not telling you that they don't have some ability at some time to go back and get involved," he said.
"But they also have an ability to get killed if they do that," he added. "And I don't think anybody should doubt the capacity of Americans to protect Americans."
Several GOP leaders, including Sen. John McCain, R-Ariz., have argued that the released prisoners have the potential to harm Americans.
"These are the hardest of the hard core," McCain said last week. "It is disturbing that these individuals would have the ability to re-enter the fight."
"They are big, high-level people, possibly responsible for the deaths of thousands," he said.