The problem is indeed not processed ingredients in cake. Unfortunately, in the US, those ingredients are not limited to cake.

And yes, most industrial, chemical, ingredients are harmless. That said, around the world, there's a emphasis on non-processed food. Unprocessed foods tend towards healthier. Less added sugar, less saturated fat etc.

I guess, taken as an overall picture, American health is perceived as poor. Poor food choices. Poor food-related outcomes and so on. That's predicated on a food culture that prioritizes cost, profit, quantity, ubiquity etc over health and quality.

Taken in that light, arguing in favor of processed foods seems like a outcome most countries would like to avoid.