First of all, a portion of the so-called Halbrook-NRA thesis may be fringe, and I am willing to suppose so for the sake of argument (and even for the sake of editing this Wikipedia article), but it is not a fringe view that Hitler and the Nazis said and did what they did.  But getting to your point, WP:FRINGE does not say "do not mention any fringe viewpoint".  Quite the contrary, Wikipedia seeks to educate people about why particular common views are fringe views.  WP:FRINGE says we should "the proper contextual relationship between minority and majority viewpoints must be clear".  It does not say "delete fringe information on sight and wage war at the talk page to keep it deleted."  In the article about evolution, for example, we have this and much more: "In the 19th century, particularly after the publication of On the Origin of Species in 1859, the idea that life had evolved was an active source of academic debate centred on the philosophical, social and religious implications of evolution. Today, the modern evolutionary synthesis is accepted by a vast majority of scientists.[49] However, evolution remains a contentious concept for some theists.[284]"