When I drink a single can of Diet Coke or anything with aspartame, I get crippling stomach aches and then sudden diarrhea, all within about 2 hrs and very predictable. It's definitely not harmless. This doesn't happen to me with stevia or sucralose, and I know sucralose isn't good for your either.

But a lot of people don't have that effect. So maybe it's not harmful for everyone.

I have a similar negative response to legumes... but billions of people eat them without issue every day.