"chemicals" (however those are defined) are bad for you, but unhealthy food is still unhealthy even if it's natural. The naturalism fallacy is just that, a fallacy.

Hamburgers aren't bad because chemicals. They're bad mostly because they're super high in calories, saturated fat, and red meat. All of those are going to contribute to heart disease, metabolic syndrome, diabetes, obesity, etc.

UPF are bad for you, yes. Not necessarily because of the processing, but rather because MOST UPF is unhealthy. That does not mean that non-UPF is magically healthy.

If you deconstruct an UPF and eat it's components, it's still unhealthy. Oreos are bad for you because it's sugar and empty calories. Not because they were made in a factory. If you just take a spoonful of sugar and eat that, that's still bad for you.

I agree that rules of thumb can be good. Here's a simple one:

- eat more greens, eat less meat