BlobPig:
Apparently artificial sweeteners are anywhere between 180 and 20,000 times sweeter than sugar. It's why they are so addictive. If you go back to regular soda it's nowhere near as sweet or satisfying (once you're addicted to it), so results in people wanting more and more sweet foods. Even though there's no sugar in them, if you're trying to fatten yourself up it's probably a better idea to drink them as you'll eat more junk food as a result.
OMG diet soda addiction is real. I had so much trouble getting off of that stuff that I will never ever drink it again. Maybe it does work to gain with, but I'm not sure if it's worth the expense.