Conclusion: Though a small percentage of people may be sensitive to it, by and large, in doses taken by people normally with their meals, it does not cause any harm.
I have read through the contents published in numerous websites regarding this topic, and by and large, they tend to agree that:
1. Glutamate is naturally occurring, e.g. in cheese, mushrooms, tomatoes,etc. The chemical form of the MSG we manufacture is the same as the naturally occurring counterpart. It does not have taste by itself, but works by sending signals to the brain that enhances the flavour of what you are eating.
2. Large amounts injected into mice show adverse effects. The amount injected is fit for a horse, which directly translates to a human needing to have an extreme overdose of MSG before adverse effects will manifest.
3. Different sources state differently regarding the outcome of blind tests done on humans. Some sources say the results weren’t conclusive, while others say that the results show the adverse effects (e.g. headache, allergic reactions, etc)
4. It must be noted that proponents of the argument may have their own agenda to advance. E.g. promoting healthy eating, organic food, etc.
5. Arguments linking adverse effects with people consuming processed foods which contain MSG need further study. It might be something else in ultra-processed foods creating these effects and not necessarily MSG.
6. Benefits of MSG advertised include adding them to healthy but distasteful food such as broccoli to encourage children to eat their greens. This could be a solution if the abstinence from healthy foods is extreme.
7. Having said all that, as per my previous post regarding this topic, I will not go crazy over it adding MSG to all the foods I eat. Eating in moderation is still key!
Bibliography against argument:
https://www.sciencefriday.com/articles/is-msg-bad-for-your-health/
https://www.healthline.com/nutrition/msg-good-or-bad#section3
http://www.bbc.com/future/story/20151106-is-msg-as-bad-as-its-made-out-to-be
https://indiatimes.com/health/healthyliving/what-s-the-big-deal-about-msg-241993.html
https://www.shape.com/healthy-eating/diet-tips/ask-diet-doctor-truth-about-msg
https://www.quora.com/Is-MSG-bad-for-your-health
(Contains arguments for and against)
https://nutritiouslife.com/eat-empowered/msg-health/
Bibliography for argument:
https://www.foodrenegade.com/msg-dangerous-science/
(Author is advocate for “real”, organic, sustainable food)
https://www.livestrong.com/article/488478-does-monosodium-glutamate-cause-cancer/
(For sensitive people only)
http://healthyeating.sfgate.com/msg-affect-health-1095.html
(Qualifies it by saying it is bad if too much is consumed)
https://www.globalhealingcenter.com/natural-health/harmful-effects-of-monosodium-glutamate-msg/
(Healthy eating advocate)
https://realfoodrn.com/why-msg-is-bad-and-why-we-crave-it/
(Home cooked food advocate)
Never Stop Learning! 