Aleksandr Kogan, the academic who was hired by Cambridge Analytica to harvest information from tens of millions of Facebook profiles, defended his role in the data collection on Sunday, saying he was upfront about how the information would be used and that he “never heard a word” of objection from Facebook.

Yet Mr. Kogan, 28, a psychology professor who has found himself cast as the villain by both Cambridge Analytica and Facebook, expressed regret for his role in the data mining, which took place in 2014.

“Back then, we thought it was fine. Right now my opinion has really been changed,” he said.

“I think that the core idea we had — that everybody knows, and nobody cares — was wrong,” Mr. Kogan added. “For that, I am sincerely sorry.”

[Read The Times’s coverage of how Trump consultants exploited the Facebook data of millions.]

Since the full scope of Cambridge Analytica’s data collection was revealed last month by The New York Times, both Facebook and Cambridge, a political data firm, have been under intense scrutiny and eager to shift the blame to Mr. Kogan.