The only reason why I mentioned that is to suggest that I know what I proper amount of MSG to add for seasoning is. The amounts in those studies are very excessive and unrealistic.
"The amounts in the studies don't conform to my culinary preferences" doesn't amount to "MSG doesn't cause headaches".
If the small amounts of MSG that you prefer caused headaches in a significant fraction of the general population, it would not be usable at all, and we wouldn't be here talking about it.
There is a combination of circumstances: most people seem to tolerate larger amounts, whereas a few people don't. And, outside of carefully controlled name-brand processed foods, misuse can happen: the problematic quantities are not that far-fetched. A stray teaspoon here or there can be critical.
It's a recipe, pardon the pun, for a controversial issue.
I use peanut butter myself; people who have problems with it are just a bunch of flakes making it up. My personal experience is all that is real.