Should language follow fixed rules of correct usage?

Axis: descriptivist: usage decides ... prescriptivist: rules decide

John

date	change	position	video
2010-07-24	new	John holds that grammar and spelling, though their importance can be exaggerated, exist to make communication clear, and that not valuing language degrades public discourse.	Grammar School with Snooki 00:00:35
2010-09-30	new	John holds that grammar and pronunciation exist to make communication clear, and that snotty correction defeats that purpose by making people afraid to speak.	MY FRIEND CHESTER 00:02:17
2011-10-19	new	John values clarity in written language but thinks debating the Oxford comma wastes finite human attention.	Question Wed--THE COVER OF THE FAULT IN OUR STARS! 00:01:32
2012-03-20	new	John says grammar's purpose is to make language as clear and intelligible as possible; using it to humiliate people in YouTube comments annoys him.	Sharpie Face Question Tuesday 00:01:06
2013-08-03	restate	John insists on 'who', not 'that', for people, refusing to accept the spread of 'that' (Hank: 'That's just how we talk, now').	Esther Day 2013 00:00:40

date	change	position	video
2010-09-28	new	Hank holds that correct usage and pronunciation matter: saying things wrong is embarrassing, and confusing distinctions like affect and effect are important to figure out.	Stop Embarrassing Yourself 00:02:46
2013-05-03	refine	Hank says both pronunciations of GIF are correct and correcting people on it makes the corrector the only one who is wrong.	17 Rants in 4 Minutes 00:02:09