According to this paper [PDF], the calculations of spiral galaxy spin which required the dark matter fudge factor were oversimplified. If you actually model the spiral arms in detail the results match observations without the need for dark matter:
"Abstract The gravity fields and rotation curves of whirlpool galaxies with thin disc distribution of material are calculated numerically. It is proved that the gravity field of mass thin disc distribution is greatly different from that of spherically symmetrical distribution. As long as the Newtonian theory of gravity is used strictly, by the proper mass distributions of thin discs, the flat rotation curves of whirlpool galaxies can be explained well. The rotating curve of the Milky Galaxy is obtained which coincides with practical observation. In this way, it is unnecessary for us to suppose the existence of additional dark material in the illuminant discs of whirlpool galaxy again. Meanwhile, in the space outside the illuminant disc, the quantity of dark material needed to maintain the flatness of rotation curves is greatly decreased. By considering the observation fact that the quantity of non-luminous baryon material is 3~10 times more than luminous material, we can explain the flatness of rotation curves of whirlpool galaxies well without the hypotheses of non-baryon dark material. So it is unnecessary for us to suppose that non-baryon dark material is about 5 times more than baryon material in a single whirlpool galaxy, no mater [sic] whether non-baryon dark material exits or not."
(Score: 5, Insightful) by Anonymous Coward on Sunday January 22 2017, @08:33AM
The paper is from 2009, didn't appear in a peer reviewed journal (ie couldn't pass minimal fact checking by experts), and hasn't even been cited in that whole time. At best, this is crack-pot stuff.
Link to article's page: https://arxiv.org/abs/0903.1962 [arxiv.org]
Link to main U.S. astronomy search engine page for it: http://adsabs.harvard.edu/cgi-bin/bib_query?arXiv:0903.1962 [harvard.edu]
(Score: 2) by patrick on Sunday January 22 2017, @08:45AM
Obligatory. [xkcd.com]
(Score: 0) by Anonymous Coward on Sunday January 22 2017, @09:00AM
It's what the mainstream won't tell you (c).