L-glutamate, the major neurotransmitter in humans, becomes excitotoxic when present outside of protein in excess of what the healthy human was designed to accommodate. That excess is readily available to consumers who ingest multiple free-glutamate-containing ingredients during the course of a day. They will be found in all ultra-processed food, meat and poultry substitutes, protein drinks, supplements, pharmaceuticals, and even Infant formula.
The “Dose dependent toxicity of glutamic acid” tells the story.
Reference
Samuels, A. (2020) Dose dependent toxicity of glutamic acid: a review, International Journal of Food Properties, 23:1,412-419, DOI: 10.1080/10942912.2020.1733016