I might be wrong about MSG. IIRC animals produce the D- entantiomer (MSG is chiral), and industrially produced stuff is D- and L-, and apparently L- can be harmful.
So, I was a little unclear: I offered two arguments against the CRS/MSG connection: first, that MSG is a scary-sounding name for a chemical that plays a central role in our metabolism and nervous system; second, that studies have attempted to isolate MSG as a cause of CRS and failed to find a link.