It is not the size of the drink that should be banned but rather the toxic High Fructose Corn Syrup in the drink that should be banned. If people want a large drink that should not be for the government to dictate. The toxic ingredient in the drink should be regulated though.
New York City Department of Health describes how drinking one 20 ounce (560ml) sweetened soft drink a day translates into eating 50 pounds (22.6kg) of sugar a year. He means Fructose. He says Sugar but he means Fructose.