And this is why I've always thought it is is important to fight prescriptivism in all dimensions, even its more justifiable or respectable dimensions. Linguistic prescriptivism is a gateway drug. Some people (editors, for instance) can handle prescriptivism responsibly because they to it as a job.
But if you take on the mantle of prescriptivism as a hobby, you may find that slowly morphs into yet another way to prove your own superiority, and then just a way to prove others' inferiority. We all must stay cognizant of how we drift over time, and to fight against the bad currents.
Sorry for ranting. I hope to turn this into a proper and more readable post if I ever do resurrect Motivated Grammar.