Appeal to Nature
There’s nothing inherently wrong in appealing to nature as part of an argument, but it becomes a red herring logical fallacy when it turns into an unwarranted assumption. The form of the logical fallacy is:
N is natural.
Therefore, N is good or right.
U is unnatural.
Therefore, U is bad or wrong.
A medicine made with “all natural” ingredients could well contain arsenic and uranium, which hardly qualify as safe. The definition of “natural” itself can be twisted using judgmental language, which you’ll see in various arguments against homosexuality.
But that’s just a load of santorum.