There are two oddities associated with concerns about the Wikipedia in the school setting, when teachers do not permit the students to use Wikipedia as a source.
The first difficulty is that the Wikipedia is often compared to the Encyclopedia Britannica, a resource I was not allowed to cite in highschool, though it is now presented as the gold standard of authority relative to the messiness of the Wikipedia. The second is that students will use the Wikipedia -- just as I used the Encyclopedia Britannica in my youth and continue to use reference works today. (In fact, I think highly of professors who can provide a good reference work or textbook for their domain, and poorly of those who can't or refuse to because they feel their topic cannot be "reduced.")
Even in high school, when confronted with a rule prohibiting the citation of a reference work I felt as if I was being encouraged towards plagiarism, or at least unfairness. If a reference work points me to a more authoritative source, should I at least not acknowledge this bit of help? Particularly, if I'm more likely to be influenced by the summary provided by the reference? Additionally why would any book among the thousands published a year be any more authoritative than a general reference work on the sole basis of its form? I could compile a multipage bibliography of books denying the Holocaust, but find few -- if any -- general-purpose reference works that did the same. The generality of the reference work insulates it from partisan pressures because it must appeal to a wide audience over many topics. It is unlikely that neo-Nazis would publish a useful general reference work for the sole purpose of shifting articles on Jews towards their perspective. However, this is not to say that reference works have no bias. Only, that if we look at the formal genre of a text only -- which is what this rule does -- any given reference work is less likely to be "eccentric" than any book taken at random.
Finally, when one considers in what direction the authority flows, books are often demonstrated as authorities by being cited by the encyclopedia! Or, at least, encyclopedias imparts as much authority to the books they cite, as they obtain in citing them -- this transfer is mediated by the reputation of the publisher, editor, and contributors.