I think it is the over-consumption that is the issue. Any acidic effects would likely be more the stomach irritation or acid reflux it aggravates in some people. I don't think this is the same as the acid/base issue some people react to with regards to the anion and cation salts processed by the kidneys.
Generally sugars are considered to be near neutral as are fats as they do not have the protein, phosphorus, chloride, and organic acids that are acidic nor the magnesium, potassium, calcium, sodium, and bicarbonates that are basic.
Actual PRAL values (for 100g of food, negative is basic):
brown sugar: -1.2
white sugar: 0 (neutral)
At typical doses even insane Western intakes we can assume this is zero. A 100g serving of meat runs at around 8 or so and a veggie serving around -(4-5) (spinach is -(12-14)). The brown sugar and honey values are obviously from mineral content, in the case of brown sugar from the remaining molasses.
Fruits have sugar, some quite a bit, and they are all basic in terms of the potential renal acid load (PRAL) or net acid excretion (NAE) measurement/calculations. The mistaken assumptions seem to come from old bomb calorimetry data where the ashes of the burned substances was indeed acidic.
So pure sugar is neutral acidity-wise and other forms are slightly basic. Take that nutritional nutjobs.