The processed a food is the more likely you’re eating a “Product”, i.e. something that’s been designed to consumed and enjoyed.
I don’t say that as a necessarily bad thing. We’ve making foods more enjoyable for the history of civilization (broccoli was bred by humans from a wild cabbage) but industrialization has given us an ability to create new things faster than our biology can adapt.
The other analogy is to think of UPF, especially nominally nutritious ones like protein bars, as the nutritional equivalent of power tools. They can be really powerful for dialing in your macros or taste desires. But must be used carefully and are potentially dangerous if untrained.
There needs to be some good (not 20 people for 2 weeks) studies which compare the effects of "ultraprocessed food" vs "really tasty food", keeping total kcals constantly high. My guess is that a high proportion of the negative effects come from an excess of salt, sugar and fat (and too many calories in general) - which is precisely how they get the food tasting so nice in fancy restaurants.
I'm also sure there definitely are chemicals we're consuming in UPFs which are bad for us, but a lot of them are probably fine. Lumping everything together so it's possible for people to get the idea that an organic yogurt is somehow just as bad as a tube of Pringles seems counterproductive.
When you look at society today, it's going downhill in terms of overall health in a multitude of ways across both the physical and mental/psychological domains. Lowered testosterone, increased obesity, increased mental illness, decreasing IQs [1], and so on endlessly. And if something like e.g. processed foods ends up being one of the factors in this, it may well be another one of those things that's basically impossible to actually prove - outside of extremely long-term correlations which can be endlessly challenged, exactly like this article is doing.
And the correlations in this case will be even easier to challenge. Like you mentioned processed foods are enjoyable to eat. They're made to generate profit and so hone in on every little receptor, desire, and impulsive (or even addictive) tendency in our bodies. People are only going to avoid this if they're already substantially health conscious, so even observational correlations can be trivially challenged. So how can we ever hope to prove anything, especially when there may be every reason to expect absolutely zilch will show up in short controlled experimental trials?
[1] - https://www.sciencedirect.com/science/article/pii/S016028962...