The headaches are real, but it's a similar pipeline/effect to caffeine/theobromine. Your brain wants at least a little MSG in your diet because it does exciting things with it. Your brain is also easily over-saturated with it and gets "hungover" if you eat/drink too much in too short an amount of time, and different people can be differently sensitive (just as with coffee/tea/chocolate/etc).
Certainly there were restaurants trying to sell you the "5-Hour Energy" equivalent of MSG and some cuisines tend to get closer to doing that naturally. But also you shouldn't directly or indirectly blame the people that make that food for you, just as it is silly to blame all coffee shops for the caffeine headaches and migraines you sometimes get if you don't watch how much coffee you are drinking.
Certainly there were restaurants trying to sell you the "5-Hour Energy" equivalent of MSG and some cuisines tend to get closer to doing that naturally. But also you shouldn't directly or indirectly blame the people that make that food for you, just as it is silly to blame all coffee shops for the caffeine headaches and migraines you sometimes get if you don't watch how much coffee you are drinking.