Here's the FDA's stance on it: https://www.fda.gov/food/food-additives-petitions/questions-and-answers-monosodium-glutamate-msg
Based on the current evidence, it is considered generally safe. MSG is found in natural food sources, like tomatoes. Originally MSG was taken advantage of in Japanese sea-weed broths to make food taste better. Think of it as like a condiment.
People before complained of the "MSG symptoms," like a tight, burning feeling on the face--this was investigated and they didn't find a link between MSG and asthma exacerbations. The flaw is that there's scant on this, so this doesn't indicate an answer.
Another study states that they found little to no effect on MSG's effects on the human's gut flora.
The studies that suggest it's the cause of some disease or cause defects to the fetus, are conducted on lab rats; these authors call for more research on MSG's effects on humans.