"It's like painting a bulls-eye on your T-shirt and saying, 'Here, aim,'" Meselson said.
During the questioning period, one audience member received scattered applause upon asking whether U.S. attacks on targets in Yugoslavia and Sudan were themselves a form of terrorism.
Carter said the question was an important one.
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"One person's terrorist is another person's freedom fighter," he said. "I don't rule out that governments can't behave terroristically."
Attendees said the event helped them appreciate the dangers Americans may face from large-scale terrorism in the future.
"This increased my awareness," said Jeff Roquen of Boston. "I don't think anyone would deny this is a possible threat to the future."