The troubling thing with professors not allowing students to cite wikipedia is the underlying truth that the debate hints at: everything you read anywhere has spin, misinformation, and exaggerated half-truth built into it.
You can’t trust anything you read, unless you can prove the truth behind it. If your proof is Google PageRank style “Well these four authors say its true, so it must be..”, then you’re standing on a house of cards.
The troubling part is that some authors dare to claim they author non-fiction.
The truly troubling part is that we listen to such “news” and accept hearsay/spin as fact. We then internalize it, compile it into belief, and then act on belief, retelling the story to our peers via the grade school telephone game.
History is (re)written by the winners with the most charismatic leader. That, I dare say, is fact.