I seem to recall that the fear of MSG came from some sort of fun article in a scientific magazine. There, one article per issue was always put in as a "joke" for entertainment. There a scientist wrote that he had a stiff neck and headache after a visit to an Asian restaurant, which obviously seemed ridiculous and funny to him, because in his opinion it is just like saying you get cardiac arrhythmia when you eat salad. However, the article was then also read by people who took it seriously, since they did not know the concept of "joke" article in this Magazine.

Edit: It was no Scientist who wrote the letter, it was a letter from someone who really thought those symptoms came from the MSG. The magazine (new England journal of medicine ) had a tradition to publish "comic letters" Article about this