What the Fallacy?!
Appeal to Nature
The Fallacy
Making the argument that because something is 'natural' it is therefore valid, justified, inevitable, good, or ideal.
Why it's wrong
Many 'natural' things are also considered 'good', and this can bias our thinking; but naturalness itself doesn't make something good or bad. For instance murder could be seen as very natural, but that doesn't mean it's good.
Example
The wilderness guide refused the antibiotics for his infection, claiming that since the bacteria were natural, his body should fight them off naturally without 'chemical' interference.