Your brain on glutamate: "Wow, this essential neurotransmitter helps me think, learn, and form memories! Amazing biological marvel!"
Your brain reading "monosodium glutamate (E621)" on a food label: "DANGEROUS CHEMICAL! ALERT! ALERT! WE'RE ALL GONNA DIE!"
Meanwhile, it's literally the same molecule just hanging out with a sodium ion. Chemistry doesn't care about your food label paranoia.