I don't think it's fallacious to appeal to nature. Sure, not all things natural are good for you (deadly viruses etc.). But when you have something that works for millennia, and has been optimized (by evolution) for that specific purpose, making changes to that specific thing is likely to ignore the context in which that specific thing was created. It's like trying to change a legacy software system with no documentation. You have to be very careful not to introduce bugs, and in most practical cases, "how the legacy system does it" is GOOD, and you should hold the burden of proving that the new system is actually better.