We really are not in a good position to assert what foods are "healthy" and which are not. Many long held views on things like saturated fat simply don't hold up when you view the ingredients in isolation. Research on health factors related to food is incredibly difficult to do.
That said, we can look at proxies like "what do healthy people tend to eat more of?", and the clear evidence is that people that are healthy by and large have diets that are low in UPFs and high in home prepared food. Of course, this could be a correlation, but until we have this properly established, the precautionary principle would be that we shouldn't eat too much in the way of UPFs, because that necessarily also implies food prepared and cooked in a way we know to be correlated with health. We certainly shouldn't be pushing it on our children.
There's no circularity. You asked me what processing meant and I said what it says in the legislation, which is pretty similar to the Nova classification. That definition was used because it's broadly useful without being overly restrictive.
By all means use MSG - nobody is stopping you. But there's a good hypothesis that MSG is problematic precisely because it is one thread of hyper-palatable food. Of course soy sauce or miso contain plenty of MSG (or at least a close analogue), but they also tend to influence flavour so are hard to use to excess; they also cost more so there's an cost pressure to limit excessive use.
The whole discussion here is how the legislation's definition is lacking, because it excludes otherwise perfectly healthy foods.
You tried to clarify it by saying "it's about processing", and when pressed, said the definition is what the legislation says it is.
You see how this is circular?
> By and large it's ingredients most people use and recognise in their own kitchens
I have MSG in my kitchen. Does that make it ok then? An "ultra-processed" food becomes "ok" if people just... see it more often?
This is exactly the sort of blanket BS the OP was talking about.