Possibly carcinogenic, but that's a big possibly, compared to the blatantly obvious harm caused by high-fructose corn syrup.
Or are you talking about other ingredients?
Even the studies of them being bad for "getting used to sweetness" and thus making people more obese through compensatory over-eating are studies that rely on self-reporting and polling.
When properly controlled, physics works as it always has and you can't magic mass or energy out of thin air.