MSG can be seen plainly on Kombu, used for making Dashi, and also in mature Parmesan if you hold it up to the light. It is certainly a naturally occurring and reasonably naturally produced substance. The reason for the reactions people experience with it is entirely to do with massively exaggerated use, and the symptoms are pretty similar to those caused by serious oversalting. MSG actually has a strong taste, but if this taste is identifiable in a finished dish it has been overused by at least a factor of ten by cooks whose judgement has been destroyed by overexposure. It has its place, used with discretion- a pinch in a large panful of chinese style chicken stock makes all the difference in a way that more concentration, which makes something too gelatinous for its purpose,does not, and most importantly reduces the apparent need for excess salt.
I use it almost never but do keep some in the kitchen-it is infinitely preferable to commercial stock cubes, pastes and granules for instance, and I am sure both less harmful and less corrupting to the palate.
And it has to be said that the bizarre 'ma-la' sensations found in the Sichuan kitchen do not quite happen in the same way if there is no MSG there.
