I don't know that it is a fallacy but it is a trope:
http://tvtropes.org/pmwiki/pmwiki.php/Main/NobleSavage
enjoy,
Rhizo
Quote:A character who is portrayed as nobler or of higher moral fibre than the norm, due to their race or ethnicity, which is that of a barbaric or savage tribe. (Often regarded as living the Good Old Ways). The savages in question are quite often American Indians, so you could probably call them Mary Sioux. Rare nowadays, except as a Sci Fi alien- though it has made something of a comeback with the idea of Magical Native American people being more in tune with nature than the greedy white people. Unfortunately still considered normal in academic anthropology (albeit not as much as it once was), despite being/becoming discredited in popular media.
http://tvtropes.org/pmwiki/pmwiki.php/Main/NobleSavage
enjoy,
Rhizo