OK, so. First off, Melville Dewey was a sexist, racist, anti-semitic creeper. He was an advocate for women getting into libraries, and helped found one of the first library schools at Columbia. This was mostly because he felt women were suited for the “repetitive nature” of library work at the time. He also thought they were more easily controlled and “didn’t cause trouble”. So, ew.
It is not possible to represent the full spectrum of human knowledge, we know that now, but you can tell a lot about what people find important by what they choose to privilege within the types of classification schemes they create. For example, Ranganathan was remarkably abstract, using things like personality, matter, energy, space, and time as sorting facets for his Colon Classification schema.
The Dewey Decimal System (DDC) is much more concrete, but in ways that give short shrift to an awful lot of the world. Everything about the DDC is appallingly Anglocentric. If you take a look at the 200s, where religion is classified, you will note how many subclasses are devoted to Christianity. Every single other religion in the world gets relegated to the 290s. And language and linguistics! Everything non-Western gets relegated to the 490s. The 800s are devoted to literature. One guess what happens there.
Given that DDC is used mostly in public, school, and smaller libraries that don’t have enough books to warrant a classification system as complex as Library of Congress, one wonders what sorts of values are being imparted by the emphasis on Anglo/Eurocentric everything. Obviously these things can be overcome, and nobody would ever accuse the DDC of causing the devaluation of non-western ideas or thought, but it’s just one more subtle structural fuck you.
[eta 3/19/2015] Which is not to imply that LC doesn’t also have biases. Please see the middle of this talk by Chris Bourg, director of libraries at MIT, for examples. These are manifestations of biased systems in general, not just classification schemes. [/eta]
To be honest, it’s mostly institutional entrenchment that hasn’t lead to any sort of reform. (Insert rant on how you can put ten catalogers in a room and come out with twelve opinions.) Librarians are well aware of its flaws, but it would be a tremendous effort to overhaul the DDC. And asking people to implement those changes, in an age of declining appreciation for libraries and thus staffing levels, would probably not be the best use of those limited resources.
There are alternative classification schemes formed in opposition to DDC for various reasons, including the lack of inclusivity, the most notable being BISAC, which is based upon subject headings used by booksellers. The problem is these systems have not been evaluated particularly thoroughly, even by the institutions that use them. And they are not suitable at all for libraries with large collections (but most of those use LC, which is its own can of worms).
That was probably more than you wanted to know. :D