On an individual level where diet soda is replacing regular soda, or where diet soda is used as a treat when controlling caloric intake otherwise I find the generic “diet soda is bad for you” to be misleading enough to be wrong.
The “woo” is that usually it’s not some commentary about artificial sweeteners increasing caloric intake, but some nonsense about artificial sweeteners being unnatural or causing cancer, etc. it’s not too dissimilar from 5G warnings or anti-vaxx.
Large observational study referenced in this article:
https://www.psychologytoday.com/au/blog/the-red-light-distri...
Some decent primary sources in this article, specifically interventional animal model studies:
https://ketodietapp.com/Blog/lchf/artificial-sweeteners-the-...
This interventional study was ended early on ethical grounds because the depression caused by diet soda was too severe:
It's relevant because controlling caloric intake without relying on the bodies natural hunger signals seems to be close to impossible for most people. The alternative is to ignore your gnawing stomach all day and carry a food scale to every meal. Only the most dedicated athletes can sustain a routine like that. Everyone else eats until they are satiated and will gain weight.
There's an obesity epidemic in the US and discounting mounting evidence of a substance modifying our eating habits in a potentially unhealthy way as "unsubstantiated woo" strikes me as counterproductive. We should be taking a very critical look at the American diet as something is wrong.