Shouldn't we take the opposite approach? Make it very hard to use highly processed unnatural products, to the point where it's cheaper and easier for companies to fall back on less processed "clean label" ingredients.
I work in (well, adjacent to) the F&B sector and I can tell you that every large company knows exactly what clean food means, why it's healthier, and where to source the ingredients, and that they have equivalent food products using these either already on shelves, or waiting to be produced if there's a shift in consumer desires.
The reason that they don't already use them - the reason you mostly only see advertising for processed foods - is because the more highly processed a food is, the higher the profit margins for companies. I've seen it stated as a rule that every level of processing gives a 2x profit margin. So if you can process an item 3 times, you'll 6x your profit margins (obviously a rule of thumb rather than law).
How about only put things in food that are contributing to the actual food? It's not just nutritional value, it's absolutely taste and texture as well. But visuals? Surely you can agree the balance of "is it worth it" is different for the color of a fruity loop than for nutritional value and taste.
You're correct that the "acceptable" line needs to be somewhere because risk isn't absolute, but that line can be in different places for different purposes. (And you can't just write off all cancer concerns because some of them probably aren't legitimate.)