Well... that's arguable and has been arguable since it was created. But arguments I have read aren't always good enough for one side or the other.
Even though anyone can edit it and insert incorrections, the articles are quickly corrected by maintainers and visitors. I've seen this happen in real time while I was browsing the wikipedia. Off course this depends on the article itself and the attention it gets from other users. What if when we last read it and acquired information it was wrong and only corrected after we closed the browser? In my opinion it's up to the reader to cross check the information before using it in an important project. But this is also true for most scientific papers.
This is one of those views , against citing the Wikipedia, that misses the point. Quoting:
"Yet as I say to my students, 'if you had to have brain surgery would you prefer someone who has been through medical school, trained and researched in the field or the student next to you who has read Wikipedia'?"
Well... (this might seem obvious to the reader but I guess not to this professor) wikipedia is not supposed to be an alternative to a medical school! I wouldn't like a reader of the wikipedia to perform brain surgery on me but I surely wouldn't be interested either if it was a reader of the Encyclopædia Britannica or any other encyclopaedia or the best medicine or brain surgery manual in the world for that matter.