Without properly establishing that diet soda is necessarily better than regular in all situations, then assertion that one can stay with regular has legitimate cause. If they are about the same, then either can be consumed without any discretion or care whatsoever.
This is the old "burden of proof" argument. Each side claims the other has the burden of proof. Just because one simple aspect (on rats) was isolated and tested, doesn't make the claim that "both are equally bad" a true statement. It is true only in that test and context. My argument would be that the burden of proof is greater for those who believe that diet soda is worse than sugared soda. But, then you will claim the burden of proof is on me and that argument never really goes anywhere, in religion, science, or otherwise.
Additionally, not all diet soda uses artificial sweeteners. Stevia, comes to mind, which is a natural product. You would mean to tell me that sugared soda is still better than a diet soda sweetened with Stevia? If so, can you back up that claim?
I won't get roped into an endless retort, not worth my time, nor yours. If science becomes advanced enough to factually state that in X,Y,Z circumstances S is better than D - sure, then we must accept that. We are FAR, FAR from that. That leaves us with anecdotes and common sense. Plenty of very healthy people drink diet soda. What is your explanation for that, if this is universally bad? Specifically, why am I perfectly healthy, despite the fact that I supposedly drink this "poison"? Again, not gonna get roped into an endless debate where nothing can be proved beyond citing correlative studies that don't use controls and proper reporting. Most studies, micro or macro have nowhere near the level of detail required to make any matter of fact statements. So, I don't see why one should be extremely dogmatic.
On a side note, I'd like to read the actual study for myself. Too many questions, and that site is actually just a commentary on it (Oh, that isn't a criticism, I do the same thing)
Anyhow, two quotes I really loved from that:
What does this mean for the average consumer of artificial sweeteners? As the study was performed in animals and not humans it would be wrong to draw firm conclusions about what might happen in people. The findings of the study do, however, add to the growing body of research that suggests that sweeteners are not benign alternatives to sugar.
I agree, it isn't benign. My whole argument, thus far, and always has been one of realism. People will naturally crave things that are probably not the best. We should moderate that.
It is likely that the best advice is the blandest: everything in moderation. There is no such thing as good or bad food, only good or bad amounts. Maybe avoid consuming too much of either sugar or sweetener, especially in drinks.
So if you drink two sodas a day, maybe switch one out for a diet? Maybe. Or maybe, you know, just live a little and clean up the rest of your terrible diet? Most people just eat atrociously. I have a hard time believing anyone would contest me on that anecdote that is clearly visible.
People are not eating enough veggies, nowhere near enough. Way to much highly processed food. This is likely to have much much larger consequences than a moderate amount of regular or diet soda.
And, for what it is worth, this provides another interesting perpsective.
https://reason.com/2018/05/25/dont-ditch-diet-soda/#comments
I'll finish with this statement (I value my time too much, so I won't be responding further) - There are plenty of intelligent people on both sides of this debate. Both seem to cherry pick their research, or at least, claim the other side did. Both will claim the "money" behind the research. In the end, this is just ad nauseam. People are gonna do what they are gonna do, regardless. I just personally hope people look at their entire diet, not just one small part of it. Any change in a better direction is a good change IMO.