Actually, there are different contextual meanings to apply for "natural".

I know what your trying to say, but you're not accurate and are "throwing the baby out with the bathwater" as a blind rejection of the word and it's meaning.

One example that I've made in the past - birds build nests, and humans build everything else - just as naturally.

You're innate capacity to collect materials and use them without transmutation is a basic form of natural behavior. When you evolve the capacity to alter chemical compositions at will through technological developments that were further built from that basic abstraction in nature of simple collecting things to build basic survival habitats. Using fire is the start of the change. Leading to smelting of solid metals, and then technology and bioengineering, etc. There are serious dangers. People are weary of trusting the untested consequences to manipulation of food, creating chemicals that aren't (yes) naturally found in nature or in the quantity and concentration we make them.

So when you say:

anything man-made is as natural as the rest of the universe!

That's a fallacy to polarize it to that ridiculous false extent. We diverge greatly from a basic natural capacity to collect from our environment and make minor modifications, to the great power of consciousness to create things that can alter and modify our reality to a greater degree. Nuclear bombs, bioweapons, bioegneering, technologies, war, there is a long list of dangerous things we can do with the power to tamper and create. These things are not naturally there. Just because we do actions in the world, doesn't mean that all our actions are simple "natural" lol. There is a specific meaning you are trying to erase and just generalize anything that exists as "natural".

There are some things that are natural good for us, something that are not, and then we also create things that are or are not not good for us. When we create something new, it diverges from that base norm of "natural". When a bird creates a simple nest from collecting material, the material didn't really change, it just aggregated. That is a simple power to create from consciousness in another animal. Human animals have much greater power to alter, affect, change, shape, mold and create into reality. When we craete things, the degree and magnitude of divergence from the base norm "natural" is much greater than other animals. We create much more than is unnatural in that sense.

Also, organic products can also have bad man made chemicals in them. It's a gimmick. Natural things can also have bad chemicals in them. People are indeed being deceived. But there is something about knowing the product ingredients, and seeing nothing was added except for what is known 100% to be safe without any problems in any doses.

This is the base norm of nature being followed more than not, as we are not tampering too create new compounds, etc as a new product. Compared to scientifically man-made chemicals that diverge from the base norm "natural", then it's more risky when it's not even a product of nature itself, but an extracted component that we artificially created, or extracted from something else to put in another food, and it has a weird name. If we knew with more certainty what was being added, and for what reason. And things shouldn't be added to food, nor people allow themselves top purchase it, without extensive testing to determine if a new man-made creation is actually beneficial or harmful, to have customers ignorantly purchase and consume.