Mixed feelings on that one. I remember trying to impress a history prof in university by chasing after a primary source for an 18th century event. That means using an 18th century document. Great, right? Well, not really. Not only did the prof know the document, but he knew that is was unreliable. And he put a comment stating why it was unreliable then told me to stick to secondary sources until I get a better footing in the subject.
If I had used the equivalent of the Wikipedia back then (since the Wikipedia did not exist back then), I would respect his decision to fail the paper based upon the use of indadequate sources. I would respect it because I would understand that he is assessing sources on deeper criteria than "any schlep can edit it, therefore it is evil."
Because you know something, that 18th century document that I used was also written by any old schlep. The fact that it was in print, then microfiched, by a university may lend it perception of credibility but it still lacked credibility. And only someone who is familiar with the publications can make that assessment.
So if you make an assessment against Wikipedia, "it can be edited by any schlep," I cannot respect that assessment. You can say that for any source, until you have read and evaluated it. If you make an assessment against a Wikipedia article because you know the quality of that article, then I can respect it because the source is being evaluated. Of course no prof is going to allow you to use the Wikipedia because they are too intellectually lazy to bother assessing it themselves.
Of course the other valid criticism of the Wikipedia is one that is valid for any encyclopedic source: they go for breadth rather than depth. I would accept a decision based upon that criteria too.