Dante wrote:
Writing, as with speech, is about communicating. When we become overly concerned with formal rules -- many of which are in error, or whose purpose has expired -- we miss the point.
There are a few obscure things that people really should work to do properly, but they're pretty rare. The only time I'm going to bother to correct someone's grammar is if the misuse actually causes confusion (failure to use subjunctive case properly), or when his target audience is snobby enough to care about of grammar in a professional sense.
In complete contradiction of what I've said above, if you say "an historic occasion" in my presence, I'll consider sticking a spoon through your larynx.
Personally I find such predictable rationalizations of sloppy writing to be inverse snobbery - a lamentable recent trend.
There is absolutely no confusion about the meaning of "Little Johnny done so good on his English test, his professor must of been nuts not to given him an A". Judging writing only as communication, that sentence deserves an A too. It doesn't stop the sentence from being incorrect, ugly and indicative of a poor education.
Of course there are examples where breaking the rules of grammar and improper word usage are not only acceptable but even preferable. Mostly of course due to the ignorance of the audience, but still true. Outside statisticians, Latinists and economists, few people don't have to stop and think a bit when told that the data ARE positive, since everyone else expects "is" instead. And only English purists cringe any more when informed none of us are playing trivia right now, even though they are perfectly correct that, as a contraction of "not one", none of us really IS playing trivia right now. You may be uninterested in these rules, but none of us is truly disinterested.
Other rules are starting to sound a little archaic and forced too, even if generally understood to still be correct. I've had people snigger when saying things like "may I borrow a cloth with which to mop up this beer?" even when, according to the claim above, that communicates my desire with no possibility of confusion and so should be completely acceptable. Listeners would apparently much prefer the equally communicative but far less accurately framed "can I borrow (gods help us, even "lend") a cloth to mop up this beer with?".
It's not and never has been about communication or lack of confusion - it's about keeping current with expected manners of speech and word usage shared by the intended audience. There is, I surely hope, not one of you who is ignorant of the meaning and typical usage of the word "lest". Using it as I once did to an educated audience made up of engineers and senior managers, I could be even more confident that it would be universally understood. It also had the advantage of being much shorter than the normal alternative of "so that....should not..." - a positive thing in one prone to verbosity as I am. I think they made fun of me for "lest" for about six years. I took it as a compliment, but it still demonstrates that lack of confusion and communication of ideas are not at the heart of complaints about rigid rules and precise word usage. Part of the reason is inverse snobbery - the feeling that everybody should sound "like normal folk". Part is a genuine inferiority complex from those who know that they lack the comprehension and vocabulary to follow suit, but I suspect most of it is the same kind of modish groupthink that made people "hep", "hip", "groovy" and "cool", at different times, for displaying the same tendency to speak in the vernacular.