MSG and natural glutamate are not the same thing.
Well, MSG wasn't even invented until 1908, so it isn't a food with a millenia-long record behind it. It's the same reason I don't trust Canola oil: anything that has to be processed that much to make it "edible" really isn't edible.
Technically, this is correct. Very technically. Scientists refer to this as straining at a gnat. Your links provide an excellent example of how the food police (aka toxic terrorists) abuse science to create alarm.
In life, only L-glutamic acids are utilized. D-glutamic acid is a mirror image of L-glutamic acid. Your article even states that they are stereochemical mirror images. Enzymes are 3 dimensional and are highly selective. They only choose L-amino acids to build proteins. D-glutamic acid is a product of manufacturing but the body easily, and without result, metabolizes it and passes it.
The article is also correct in stating that some amines and propanols are created as a part of the manufacturing process. However, there has never been any legitimate study showing that these trace (read: minuscule) amounts are harmful in any way, which is why your article is very careful to say that they could be harmful. Nothing like the power of suggestion to create fear.
Soy sauce contains equal amounts of D and L-glutamic acid. The Japaneses have been eating it for thousands of years and still enjoy the longest life span in the world. When Hydrolized Vegetable Protein came on the market it was studied to death by the FDA and none of the issues your alarmist links cite were ever found by the FDA even though HVP is loaded with D-glutamic acid. The argument that D-glutamic acid is in some way bad for you when it is a mirror image of L-glutamic acid, which isn't bad for you, is spurious at best and is being perpetrated by frauds who have an agenda. These two molecules are identical but they cannot be superimposed. Since they're identical, how can one be ok for you to consume but not the other one?
Do you drink coffee? If so, you need to be aware that coffee contains 400 chemicals that have been identified and another 200+ that have never been identified. Of those still unidentified, some are toxic and some are carcinogenic. However, they do not exist in quantities that could be harmful to humans otherwise coffee would have been banned or warnings issued about consumption.
Thankfully, there are conservative groups like the Hudson Institute who are committed to providing factual information based on sound science to the public. Hudson is also active in exposing frauds like the Weston A. Price Foundation. (You used the Price Foundation as a link).
The whole issue of MSG being bad, in any way, is much ado about nothing. If sound-science is employed, it is very clear that glutamic acid from natural sources is no different than from "added" sources when it comes to our physiology.