The last I read about it, MSG has been a "spice" used by the Chinese for
many centuries, and is extracted from beets.
Some people do have negative reactions to it, but I'm not sure how to place
it on the scale of undesirable foods for the modern hunter/gatherer. It
has a chemical NAME but so does salt; apparently in reality it's just an
extract from beets. (I suppose the question would next be whether or not
beets are acceptable.)