Prescribing is not really the opposite of describing. Lexicographers must describe the language, grounding their definitions in real living English. Academic linguists, the arch-descriptivists, are perfectly willing to call some usages wrong and others plain ugly.
One can prescribe and preach a high-quality English while accepting variety and change. Stability is not the same as rigidity. And judgment should be empirical, not dogmatic, open to real usage and willing to change when the facts change. Getting things right is worth the effort, and so are the struggles to adapt and change to an ever-evolving language. So, cheers to modern and open-minded authors, editors, linguists and lexicographers!