First,here's a link to Carl Sagan's 1980 essay
https://io9.gizmodo.com/heres-carl-sagans-original-essay-on-the-dangers-of-cl-1481304135 Read that essay and tell me how anything he said challenges climate science today. And be intellectually honest, because I'll tell you my man, you saying that seems deceptive.
Second, why do you not mention that those people were a minority? The argument is based on a half truth.
This PDF contains a study of all peer-reviewed literature from 1965-1979 concerning climate change. Of the 49 articles that predicted changes to global temperatures, 42 predicted warming, while only 7 predicted cooling. (Note that the lead author of the 1976 cooling paper later went on to become an oil-funded mouthpiece for the global warming denier groups.)
Science doesn't follow public opinion, public opinion should follow science.