MSG is to me the poster child of most things are OK in moderation. The problem is most people are pretty terrible in practicing moderation and so they're essentially consuming super salt in large quantities which certainly can't be good for you.

MSG can really make certain dishes taste delicious, but that doesn't mean you need to dump tablespoons of the stuff into everything you eat. In Japan, many foods contain MSG; just not enough to be your weekly serving's worth.

Harold McGee on MSG: https://www.youtube.com/watch?v=k1oR0EYaOHY