I teach linguistics at university, and I can guarantee that my department would not hire anyone that cannot spell.
Professional linguists and other lovers of language *will* often be at loggerheads over what it means, for example, when President Obama says "President Bush graciously invited Michelle and I" in a speech (authentic example: that actually upset my mother). "Amateur lovers" might proclaim such things as signs of the coming apocalypse, while professional linguists will say "meh, languages change", and point out that this particular change to English grammar was somewhere between predictable and inevitable. (Which is not to say that we might not cringe a bit inside when hearing people use grammatical constructions that're gaining foothold, but that are not part of our individual grammars.) Non-professional lovers of language looks at such changes and cite them as proof that their beloved language is in disrepair, and that it has decayed from an older, more pure state. Linguists will point out that as long as there's been literacy, there've been people believing just this.
(I can enthusiastically recommend "The Unfolding of Language
" by Guy Deutscher to anyone interested in this subject matter. One chapter's dedicated to such beliefs: he gives a quote stating that today's English is completely decayed, a shadow of its former glory .. and then goes and finds what lovers of English were saying about English in those alleged glory days: the very same thing. He successfully goes back centuries like this.)
But, not everything that applies to languages applies to *language norms*, as the Standard Englishes are. Language norms aren't supposed to perfectly match people's vernaculars (and incidentally, the older they get, the further they move away from how people actually speak). They're nothing but, shall we say, agreements between a large group of people as to how one renders an acceptable middle ground between vernaculars in writing. If someone cannot, or will not, comply with such an "agreement", the message isn't a good one.
In summation: In my opinion, intrinsical
took a valid lesson from his linguistics training, but applied it where it shouldn't be applied. You can be a linguist, and still get annoyed when people mix up "there", "they're" and "their". (They're pronounced the same by *all* English speakers. Spelling them all the same doesn't make your English more evolved, it just shows that you're unaware of the underlying difference between them.)