Our bodies are extremely resilient and can take a beating from crappy foods. That's why such food 'does not kill us on the spot'.

That's the justification. If that suits you, that's fine--it's your health.

We are NOT designed to eat french fries made from genetically modified potatoes.

We are NOT designed to consume soft drinks made from high fructose corn syrup (HFCS).

Etc Etc

That stuff is not natural. Not for omnivores, herbivores, carnivores or any other living organism.

Of course we aren't designed to digest French fries and soft drinks. But to say that, simply because our bodies were not created with the preconceived notion of digesting them, we should not eat them, is silly.

I'm not saying we should eat them, but 'because we weren't designed to' is not a relevant point. We sure as heck weren't intended to eat potatoes or wheat either (rather impossible to eat without cooking, which hasn't been around forever), and they leave the diet a little deficient, yet the Irish sure did survive on them, and most of Europe built up on wheat. Would you condemn them as fools for eating something that wasn't tailor made for their stomachs? I applaud them for surviving and growing where food didn't previously exist.

French fries and soft drinks are terrible food, but the idea that there are some small collection of 'right foods' that we existed especially designed to eat is simply silly. The only time that sort of 'right food' idea is relevant, is with some animals that can only get a given nutrient one way, or animals that can only successfully hunt one type of prey.