First off, yes I'm hideously biased on the issue of guns and gun ownership in the United States (I'm for it, bring back mail order guns!) However, I also try to be objective and fact based with historical research.
Once upon a time, Michael Bellesiles wrote a book Arming America which won the Bancroft Prize, and was widely lauded as a fine work. However, in very short order, Bellesiles was stripped of his Bancroft Prize, and wound up resigning his position at Emory University over his deeply flawed, biased and possibly fabricated research. Quite frankly, I'm amazed that in 2014 anyone would even think of citing this book as a valid source, yet it consistently comes up and is presented as a viable source of information, despite having been shown to be flawed, to the point of the publisher inserting a disclaimer in the book after the scandal broke. (I've seen copies with this, it's a printed piece of paper pasted into the front of the book).
So the question, or perhaps rant, is why do people insist on presenting such a discredited source as useful well over a decade after it had been so roundly "shot down" by the academic community?
They might be unaware of the fact that the book has been academically discredited. This would especially be the case if they associate with other people who cite these works as evidence.
If they are aware they may well have fallen into the trap of assuming that the shooting down of the work was part of some conspiracy. It's essentially going "Nuh uh" to the criticisms as the work fits with your world view. In the case you cite they'd probably go "All the criticisms were just NRA propaganda." and ad hominem a few prominent critics. This goes the same the other way politically with the Tea Party affiliated having a very selective memory about the founding of America.
I think this is a good opportunity for a featured post/discussion on troublesome historians and discredited research. I know a good number of the controversies on the American side, but I'm woefully ignorant on problematic studies in European history.
I have come upon this phenomenon in Israeli-Palestinian historiography. Take Alan Dershowitz of Harvard Law. In his book The Case for Israel Dershowitz utilizes a good deal of research from Joan Peter's From Time Immemorial which was essentially a fabrication to 'prove' that Palestinians weren't Palestinians, rather a specific and quite high number had all migrated shortly before the modern conflict began. Her book is awful and represents an intentional fraud.
While this is just my opinion, I believe Dershowitz (an unflinching defender of Israel) thought no one would go that far into his sources to uncover his academic dishonesty. The whole thing is quite notorious because the professor, Norman Finkelstein, who exposed the fraud was ultimately denied tenure at his university while Dershowitz is sitting pretty still at Harvard. Read Beyond Chutzpah: On the Misuse of Anti-Semitism and the Abuse of History for a comprehensive exploration into Dershowitz's fraud.