Diet Soda, the Silent Killer?

What is this thing called diet soda? Here are the ingredients of one of the best-selling brands, Diet Pepsi:

CARBONATED WATER, CARAMEL COLOR, ASPARTAME, PHOSPHORIC ACID, POTASSIUM BENZOATE (PRESERVES FRESHNESS), CAFFEINE, CITRIC ACID, NATURAL FLAVOR

My favorite line on that list is the "preserves freshness" that follows potassium benzoate. The freshness of what, precisely? The caramel color? Not likely—caramel color for most colas comes from a chemical reaction between sugar, ammonia, and sulfites at high temparatures. Or maybe it's the phosphoric acid? Or the least plentiful ingredient of all, the unspecified "natural flavor"? In plain English, diet soda is artificially blackened water tarted up with synthetic chemicals. That anyone ponies up cash for such a thing surely counts as one of the food industry's greatest marketing triumphs.