From Librarian Avengers:
I can see why the process of creating web accessibility guidelines is so difficult. The perspectives involved are broad and often divergent. This isn’t like web standards, where you can just close your tags and call it good. Real people will be discriminated against if you screw up. The responsibility is sobering.
And actually, those last two sentences could apply to more than accessibility. Bad design discriminates against everyone who doesn’t think like a librarian!