Researchers from the University of Zurich quietly ran a months-long experiment on Reddit’s r/changemyview (CMV), using AI-generated comments to test how persuasive large language models (LLMs) could be. The subreddit, home to 3.8 million users, invites debate on controversial opinions — but moderators say the AI replies crossed ethical lines.

“The CMV Mod Team needs to inform the CMV community about an unauthorized experiment conducted by researchers from the University of Zurich on CMV users,” moderators wrote, calling the study “psychological manipulation”.

The experiment involved AI-generated responses written under fake identities — including a trauma counselor, a sexual assault survivor, and a “Black man opposed to Black Lives Matter”. These posts were crafted to sound human and emotionally resonant. Some remain accessible via an archive maintained by 404 Media.

The researchers went further by tailoring AI replies using personal information inferred from users’ Reddit history — details like age, gender, and political leaning, all generated using another AI model.

Moderators say this violated subreddit rules, including bans on undisclosed AI use and bots. They’ve filed a formal complaint and asked the university to halt publication of the research.

Reddit responded strongly. Chief Legal Officer Ben Lee called the study “deeply wrong on both a moral and legal level”. Reddit has since banned the accounts involved and is improving its ability to detect fake or AI-generated content.

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“We have banned all accounts associated with the University of Zurich research effort,” Lee said. “We’re also working with the moderation team to ensure all related content has been removed”.

The researchers maintain the study was approved by their university’s ethics board and claim it offers valuable insight into how AI could be misused at scale. “We believe the potential benefits of this research substantially outweigh its risks,” they wrote in a Reddit comment.

But CMV moderators pushed back. “People do not come here to discuss their views with AI or to be experimented upon,” they wrote. “People who visit our sub deserve a space free from this type of intrusion”.