I appreciate what you're pointing out how, but it doesn't strictly work since sugar arguably has a far larger affect on overall health and metabolism than caffeine. At least in the context of this story.
It was an eye opening discussion to say the least.
I don't even think he's saying that, actually, he seems to be saying "I don't drink soda so neither should you".
Having cut out soda, I find I have a lower tolerance for sweet food in general. I'm less likely to order sweet and sour chicken, or foods that are glazed, or things with barbecue sauce, or honey-mustard dressings or dips. I have desserts less often, and when I do, split them more ways.
As others have pointed out in this thread, most people have a sense that feeding caffeine or alcohol to kids is a bad idea; and even as adults, that they are things that should be consumed in moderation. They don't have coffee available in the school cafeteria. However, most people have no such sense about sugar, giving kids juice boxes, chocolate milks, and putting soda machines in schools for them to buy whenever they have a little extra allowance left over.
While sugar-free soda is probably an improvement over soda with sugar in it, it still leaves you with that sweet tooth, and you're more likely to subconsciously keep consuming sugars in other forms.