Earlier quoted context omitted.
It's not a backlash, it's science. See e.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892765/ While there's no conclusive proof diet soda definitely causes weight gain, there's absolutely no evidence at all that it helps with weight loss. Sugary or not, there's no rational basis for considering sodas of any variety "healthy."
Diet soda does not cause weight gain. Diet soda makes you hungrier, and that makes you eat more and gain weight.
As an aside, I have a hypothesis that naturally focusing on proximate vs. root causes is actually a big contributor to the divide between major segments of the population.