I live by something I call "The natural argument". It is very simple, and goes like this:
1. Everything is natural. Or, in its negative version; There is nothing that is not natural. Or in a third way. Everything is in nature, and therefore of nature.
2. If there is such a thing that it is, it must interact with something else. This something else, normal things, behave like any other thing, and interacts accordingly. For anything then, to interact with this other thing, it has to have the same interactions.
A little less abstractly. Let us say you had a vase, only this vase had not electrostatic forces, no covalent bonds. It would then fall through the earth until it reached the center, where it would continue to the other side of earth, and then fall backwards again. Or, if this vase in addition did not interact with gravity, it would continue along its current path at thousands of kilometers per second, the speed of the earth, functionally blinking out of view for you. And let us further say, that you were to look for your vase with a telescope, zooming out there in the great beyond, only it did not interact with light well then, you would not have been able to see it. And if this process of non-interaction would continue with the other fundamental ways of interaction with this world, the vase would then finally become undetectable to any way of knowing if it is really there - and would then cease to be a part of this universe.
3. From this we can see that there is no other way to be in nature than to interact with it. If it does so, then it is a part of nature, and has to connect to our life in some particular way.
There are some things that are barely real - like dark matter. Dark matter is so named because it, to my limited knowledge only seems to interact with our matter through gravity. You can't see it through natural light, or any other frequency in the electromagnetic spectrum. It is the very non.-interactiveness of it's being that put's it at the speculative end of "real".
Some people say that chemicals are unnatural. They aren't. Synthetically produced chemicals, which is what they really mean, are just as natural as other chemicals (everything else). What I think they mean is that they were not produced by "natural processes", by which they mean produced from the mechanisms of evolution - and I suppose that it is from this same stem that the leaf of "it is only natural for women to do carework" comes from. To these I would say simply, there is nothing that is unnatural. Our way of life is a convention, and as long as we stay within the wide boundaries of physical possibility, we are free to choose how to live ourselves.
As to the complaint about chemicals. The distinction we wish to make is if the chemicals are beneficial or harmfull. This is an important issue which I applaud your concern around.
A final issue is about the immortality of the soul. If we have a soul it has to be natural, otherwise it simply won't be real. With what we know about the natural decay of anything not built to reproduce itself, a soul outside of the body would have to find some other means of sustainment. I think it is rather unlikely that a soul would arise through evolution, because they would not serve any purpose as I could see, and I've personally seen a soul - and I don't know of anyone else who has either, so I don't think it interacts with light. In fact, I don't think the body becomes appreciably lighter after death either, so it does either not escape the body, or does not interact with light. The whole deal with the soul is looking less real by the minute to me. Sorry.
Do we need the word Natural? What useful function can it serve? I feel that we should reserve the meaning "of nature" in the slightly undefined sense to the word, and instead of using the word "unnatural", we should substitute the word "artificial", which can be either bad or good, just as natural things can be. The word pair is already still in use, as in artificial intelligence, and perhaps the sadly less used "natural intelligence". Aha....
Thank your for reading.