I can only go by my own experience with aspartame. When if first came out, at least when I first learned of it in the earlyish '80's, in Coca Cola and the sweetner Equal I was happy to see something come out of that type that was supposedly "natural". That's the way it was advertised, as a "natural" product. I used to drink a lot of Coca Cola and put lots of sugar in my tea, and started drinking the stuff with aspartame. In about a week I noticed a swelling in my lip, rather pronounced on one side. The only new thing I could think of was the diet Coke, so I stopped drinking it, and in the same week's time frame, the swelling went down. Disappeared completely.
Well, about a year later, I was again taken in by all the adverts on TV and thought I'd try again, surely it must have been a fluke!
This time, the reaction was in the same week, but it was a numb spot that began on my eyebrow, at the end, and over the next several days the same numb spot progressed along the eyebrow's bony ridge. I could literally knock on my eyebrow and not feel it.
I stopped the diet stuff again...in the same week's time frame the numbness left me.
I'll never ever try it again I can tell you. Perhaps I have an allergy to it, perhaps it is as bad as some of the websites say. I don't know. I only know that it affects ME in a disturbing manner.
That's my evidence, I may be stubborn, but I don't need a brick wall to fall on me. At least not twice.