If 'the science' is so conclusive, then maybe a single link to a single study would be an appropriate response.
The UPF definition includes a ton of very distinct things. It is unlikely that emulsifiers, preservatives, food dyes, added sugar, and removed fiber all produce the same health responses. Science showing correlations between UPF consumption and health outcomes also don't tend to show a dose response, which is odd. We'd expect lots of UPF consumption to be very bad and for some UPF consumption to be kind of bad, but we don't tend to see this in the data.
Nutritional research is also enormously difficult to perform. Any sort of controlled study is necessarily over short periods of time. Long term studies come with all of the messy confounds that make it remarkably difficult to determine causation.
And I really don’t understand your point at all. All science starts with observing a correlation and deducing a cause years to centuries later.
But you don’t wait for newton to start believing in gravity
Existing published research has not consistently found a dose response.
The authors are also not just saying "hey here is some science." They are advocating for policies that say that plain potato chips can be in schools but sour cream and onion potato chips cannot.
You’re welcome to do your own years of research to learn more (everything, cooking, freezing, drying, blending, adding acids affects amino acids and certainly bacteria in the food) but until then stick with what the studies prove