I call BS. I know sugar is hard on your body -- but drinking 12oz of water with 10 tsp. of sugar in it doesn't make me or anyone I know want to vomit, so I don't see why Coke without phosphoric acid would.
Coca-Cola isn't good for you. It's high in sugar, has minimal nutritional value, and its acids are terrible for your teeth. However, the amount of sugar in it is not out of the ordinary (when compared to 100% juice products). In fact, grape juice has nearly 50% more sugar.
For example, grapes are 52% fructose, 46% glucose, and 1% sucrose. Pears are 63% fructose, 29% glucose, and 8% sucrose. High fructose corn syrup used in sodas is usually 55% fructose and 42% glucose.
The "natural" sugar you're thinking of is sucrose. Sucrose is not the dominant sugar found in fruit. Fructose and glucose are the predominant sugars found in fruits and in high fructose corn syrup.