If there's anything wrong with MSG that isn't simply due to sodium intake, I think it's unknown to science (at least in the sense that there's no theory about it with any wide uptake). MSG is also intensively studied and has a very similar mechanistic story to aspartame.

Sure, but it feels like a silly distinction. The famous example is water, which fits those same criteria. Would we that that there's not "nothing" wrong with water?

The same This American Life episode raised serious doubts about Dr. Steel's claims, which is mentioned in the article you link:

> When reporters tried to corroborate Dr. Steel’s claims, however, holes started appearing, according to the This American Life episode. Chief among them: There actually was a real Dr. Robert Ho Man Kwok, and his biographical details seemed to match those provided in the letter, like his professional title, the name of his research institute, and the date of his move to the US.

> While both Dr. Steel and Dr. Ho Man Kwok had died by the time the digging began in earnest, their surviving family members were able to shed some light on the situation. Dr. Ho Man Kwok’s children and former colleagues were adamant that Dr. Ho Man Kwok had in fact written the letter. Meanwhile, Dr. Steel’s daughter said her father was a lifelong prankster who loved pulling one over on people. With this testimony in mind, the reporters came to the conclusion that Dr. Ho Man Kwok was most likely the true author and Dr. Steel had taken credit for years as an elaborate practical joke.

I have a family member who has discovered through gradual process of elimination that she gets migraines from MSG, aspartame and yeast extract. "just sodium headaches" doesn't really apply to her case; simply chewing a piece of gum that has aspartame, or eating a piece of meat cooked with MSG in her salad is enough to trigger them. I agree in the general sense with your comment and the article that there's no widespread danger to public health from these additives, but it doesn't mean there aren't still individuals whose health gets messed up (including legitimate headache or migraine symptoms) by these additives.

This effect is very obvious on me. I consistently get headaches when my sodium intake is too high. I don’t even use MSG in my own cooking but occasionally I add too much salt.

I drank sodas with aspartame just fine for many decades. Then one day they suddenly started giving me migraines any time I had one, so I had to quit cold turkey. No other amount of caffeine, regular sodas, salty foods, MSG-laden meals etc. seem to trigger it though, and I have no idea why.

> So a little MSG to get your taste buds extra sensitive to other flavors is a net good.

Salt and MSG are sometimes said to strengthen existing flavors, but I'm pretty sure they mainly just contribute their own unique taste: salty and umami.

(There could of course theoretically be some interactions with other taste receptors, similar to how sweet things make things taste much less bitter, e.g. cocoa, but that is a relatively specific effect and not one that acts as a general flavor enhancer.)