The Time Magazine cover story in 1984 where they falsely claimed that consuming cholesterol from eggs and other sources was dangerous was a real turning point. That misunderstanding has caused tremendous harm to public health for decades. I think the journalists acted in good faith but they believed junk science.

https://time.com/archive/6855517/hold-the-eggs-and-butter/

https://content.time.com/time/specials/2007/article/0,28804,...