A popular explanation for the origin of reservations against MSG is that it came from a letter from 1968 coining the term “Chinese restaurant syndrome” by a Dr. Robert Ho Man Kwok (apparently a pseudonym although a Dr. Robert Ho Man Kwok existed) and is just xenophobia.
It seems like a bit of a contrived argument that all the mistrust stems from a letter and xenophobia. From my understanding Asians themselves also commonly view MSG as being unhealthy.
https://news.colgate.edu/magazine/2019/02/06/the-strange-case-of-dr-ho-man-kwok/
The "Urban Legend" is likely accurate
The Account in the Colgate article is contested, and I do not find it credible.
An orthopedic surgeon, Dr. Steele, claims he wrote the letter under a pseudonym. However there was a real Dr. Robert Ho Man Kwok, a senior research investigator at the National Biomedical Research Foundation and a Chinese immigrant. Kwok passed away prior to Steele going public with his claim of staging a hoax, but Kwok's children have gone on record saying their father wrote the letter and was proud of it (this controversy was the topic of 'This American Life Ep. 668 The Long fuse')
The episode of this American life indicates several pieces of evidence which I believe make Kwok's account more credible, the letter specifies that he has only experienced the symptoms eating "Northern Chinese food" in the United States. The regional distinction (Northern Chinese cuisine) is one an American in 1968 would be unlikely to make. Howard Steele's daughter Anna has also gone on record that she believes Kwok rather than her own father, as Steele had a habit of making wild and inaccurate claims.
The alleged "Chinese Restaurant Syndrome"
MSG occurs naturally in high levels in common foods such as Tomatoes and mushrooms. It was isolated by Japanese Chemist Kikunae Ikeda in 1908, who began manufacturing MSG as a condiment in 1909. MSG became popular in Japan, China, and other east Asian countries despite an association with Japanese Imperialism. This presents an interesting similarity to the US case, in which negative associations of 'menacing foreign imperialism' were attached to MSG, similar to the later US gloss of 'threatening immigrant exoticism.' I say this, not to detract from the brutality of Japanese Imperialism, or the reality of anti-asian racism in the US, merely to point out that food has an important sociological dimension.
US food manufacturers were already using MSG by the 1930s and by the time of Kwok's letter in 1968, MSG use was widespread in the US. Kwok's letter, in which he complained of experiencing "numbness at the back of the neck, gradually radiating to both arms and the back general weakness and palpitation" were the first time negative effects had been tied to MSG, but the letter sparked a flood of similar testimonials. However, it was published research by Schaumburg and Byck in 1969 that solidified "Chinese Restaurant Syndrome" as a alleged medical condition which was taken seriously by many professionals. The Schaumburg paper mentioned that MSG was a widely used food additive, but centered their experiment on Wonton soup. The study spurred additional research which mostly seemed to find further evidence of MSG's harmful effects. A rising public awareness of "Chinese restaurant syndrome" led to 622 complaints about MSG to the FDA's Center for Food Safety between 1980 and 1994.
Despite the prevalence of MSG in US food products, the response was heavily racialized, not only in the name of the syndrome, but in testimonials such as this 1972 statement from Actor Lorne Greene, denying he had suffered a heart attack and blaming the 'syndrome' instead:
"It was the Chinese restaurant syndrome...I went out to a Chinese restaurant for dinner and the food was de-goddamn-licious. Shrimp, beef, fried and sizzled, and like an idiot I put some more soy sauce on the rice, and that stuff is filled with monosodium glutamate. I kept talking and eating and talking and eating and suddenly I felt my stomach saying, ‘action stations’, and I knew I was in for a siege of something"
Is MSG unhealthy?
"It seems like a bit of a contrived argument that all the mistrust stems from a letter and xenophobia. From my understanding Asians themselves also commonly view MSG as being unhealthy."
Although this may seem "contrived," it is true that the mistrust of MSG in the US was shaped by xenophobia, and that the single letter sparked the subsequent research and public perception. As already noted, historical views of MSG in Asia were also affected by ethnic/national perceptions of MSG as a "Japanese" condiment. The xenophobic dimension is seen not only in the US name for the syndrome, but in how Kwok's narrow complaint about Northern Chinese restaurants in the US were generalized to all Chinese food and the the prevalence of MSG in other cuisines and mainstream food products were largely ignored.
The early research on the potential harms of MSG has been heavily qualified or debunked by more modern studies. The main studies which set off the health scare:
It is true that new research indicating correlations between MSG consumption and negative health outcomes continues to be published. I don't think these studies are effectively untangling the causality to show the effects of MSG as opposed to the effects of processed foods, added sugar, etc. But the debate continues to a certain extent, and you may find the research convincing.
Some scholars make the point that the racialized character of the early outcry against MSG has receded and modern advocacy against MSG is characterized more by concerns about processed foods and food labeling (such as this).
Kwok's letter:
First US research of effects of MSG:
Sources
Examples of modern Research on negative health implications (I am skeptical about most of this but your mileage may vary)