Its kind of like when you were a kid and said someone farted, regardless if someone did, everyone is going to leave the immediate area and say it stinks. Group think is a crazy thing, which is why I used Marijuana as a comparison, lies can be perpetuated for very long time as long as people repeat it.
MSG is used less and less as a tenderizer now since no one wants it on their food. Today these restaurants prefer to use baking soda since its cheaper and does a faster job at tenderizing, also they can say they used no MSG. The trade off is that the meat loses its flavour the longer you tenderize it.
Try sprinkling MSG sometime on a cheaper cut, dont leave it on too long or it will turn into mush.