Manning made the remarks at a conference in Nantucket that was one of her first public appearances since being released for a military prison in May. The Associated Press was the only media outlet in attendance.
"I believe I did the best I could in my circumstances to make an ethical decision," she told the crowd when asked by the moderator if she was a traitor.
The 29-year-old transgender woman was known as Bradley Manning when she was convicted in 2013 of leaking a trove of classified documents. She was released after serving seven years of a 35-year sentence, which was commuted by President Barack Obama in his final days in office.
Tom Scott, who co-founded The Nantucket Project with Kate Brosnan, said they invited Manning for "clarity of understanding."
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"My brother and father are Marines. They would respectfully challenge some of her decisions," he said.
"Barack Obama commuted her sentence. My instinct is that he's a good and trustful man. How do those two things mix? Seeing her in person offers, perhaps, the best way to decipher that."
Several audience members said they were intrigued to hear from Manning. Sara O'Reilly, a Nantucket resident who has attended several past conferences, said the speakers are typically a "little edgy." She said she doesn't judge Manning and other people have done "far worse" things. Bonnie Roseman, of West Palm Beach, Florida, said after the talk that Manning is courageous.
Manning said Harvard's decision signaled to her that it's a "police state" and it's not possible to engage in actual political discourse in academic institutions.
"I'm not ashamed of being disinvited," she said. "I view that just as much of an honored distinction as the fellowship itself."
Eugene Jarecki, an award-winning documentary director, moderated the discussion. He asked Manning if it "reflects something about the state of our time" that she's still the subject of pressure by the CIA on Harvard and labeled a traitor.
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