Saccharine (Sweet 'n Low) was the big scare back then.

It turned out it did cause cancer... in rats... if you force fed them some crazy amount like 400x normal.

https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/artificial-sweeteners-fact-sheet

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3185898/

"humans would need to drink the equivalent of 800 twelve-ounce diet sodas with saccharin daily to reach the carcinogenic doses that induced rat bladder cancer."