Eugene Volokh quotes an excellent letter on prescriptivism vs. descriptivism in language, or why it’s OK to say “NU-kyu-ler.” H.W. Fowler, author of Modern English Usage, the greatest of all “prescriptive” guides, had this to say (under the heading “pedantry and purism”):
Pedantry may be defined, for the purpose of this book, as the saying of things in language so learned or so demonstratively accurate as to imply a slur upon the generality, who are not capable or desirous of such displays. The term, then, is obviously a relative one; my pedantry is your scholarship, his reasonable accuracy, her irreducible minimum of education, and someone else’s ignorance….
Purism is like pedantry, except that it does not necessarily imply a parade of superior learning. Now and then a person may be heard to ‘confess’, in the pride that apes humility, to being ‘a bit of a purist’; but purist and purism are for the most part missile words, which we all of us fling at anyone who insults us by finding not good enough for him some manner of speech that is good enough for us…. Pure English, however, even apart from the great number of elements (vocabulary, grammar, idiom, pronunciation, and so forth) that go to make it up, is so relative a term that almost every man is potentially a purist and a sloven at once to persons looking at him from a lower and a higher position in the scale than his own.
And Fowler was supposed to be a prescriptive grammarian. My own experience with language pedants is that the less they know, the likelier they are to insist on some particular niggling point or other.
(Modern English Usage appears not to be online. As a dictionary, albeit a highly eccentric one, it would be an ideal candidate. Fowler’s other book, The King’s English, is, but it isn’t nearly as good.)