This is only one half of the story. To make an apples-to-apples comparison you also have to consider how much you need for the same effect on taste. Hypothetica

This is only one half of the story. To make an apples-to-apples comparison you also have to consider how much you need for the same effect on taste. Hypothetically, if you need 10 times as much glutamate as salt to achieve an equally tasty food, then salt would be a better option. Also LD50 only takes into account short term effects. This is the same story with aspartame vs sugar. Aspartame has an LD50 of around 5 g/kg, sugar 29.7 g/kg. You can say "wow, aspartame is 6 times as toxic as sugar!", but you have to take into account that it is 200 times sweeter than sugar. Of course in reality you can't really compare salt with glutamate since they stimulate different receptors. In the end we can probably conclude that neither salt not glutamate pose any real danger to a healthy person in doses that are not completely ridiculous, so add both to your food!