As someone who's a passable and occasionally experimental writer but a terrible editor, I face the wrath of grammar stormtroopers on a daily basis. I understand they're1 frustrations. Its2 jarring to be absorbing language and thinking about ideas, then get derailed and have to think about sloppy editing and the crisis of education. If I see 3 grammar or spelling error4 on the first page of a book, I won't reed5 it.
But the current correction climate is too harsh. Many of the rules people shout at students are just wrong, and much of the rage thrown at people for common errors is misplaced, especially in the era of "wut U up 2." So here are a few guidelines for what should and shouldn't be harped over:
It's, Its, Your, You're, There, They're, Their, Loose, Lose, Who's, Whose
People often separate these into five different errors, but they're all the same to my mind. I didn't even know there was a widespread problem with loose and lose until I saw it popping up in lists of grammar peeves. Nobody who writes regularly is confused about these words. There may be people whose jobs involve frequent communication and who really don't get it, but these people probably don't have jobs that involve describing complex ideas to discerning readers.
This is why I've grouped them all together: these mistakes are not failures of understanding, they are typos. If you're composing in your head and typing 90 words a minute, it's entirely possible you'll bang out the wrong thâr once in a while.
A simple correction will suffice. You're not helping your case explaining the difference to people who've committed one of these sins, you're just being pedantic and insulting. My iPhone corrects all "its" to "it's" and it's annoying, but if I'm tired I ignore it, because the message will still get through. It's acceptable to point out these errors when it's your job, or when you're trying to help someone polish their prose; it's ridiculous to point them out in Facebook postings, emails, memos, and texts, and it's never acceptable to explain the difference to someone unless it is your social responsibility to do so. Hint: if you aren't a teacher or a relative, it is not your social responsibility.
I could care less
This alternate, and at first glance opposite, construction of "I couldn't care less" probably arose as either a mistake or an ironic interpretation. I and everyone I know views it ironically, and if pressed will point out that few people remark upon things they care about with comments analyzing its relative position in their hierarchy of concerns. "I could care less" can safely be assumed to imply "but not without effort." This may be a bastardization of the language, but, fittingly, nobody cares.
It amazes me to no end that people who make these rules don't seem to have ever spoken aloud to another human being. Can you imagine Clark Gable storming out of the house after saying, "Frankly my dear, I do not give a damn?" Or Admiral Ackbar shouting, "It is a trap?" How about, "I can not get no satisfaction?" I spent years unsuccessfully learning all the ways Spanish words blend into each other when written, English at least has the decency to add apostrophes. Making all of your written work sound like a British law book does not actually improve the quality of your ideas or your ability to communicate them.
Never split infinitives
Splitting infinitives is fine. The languages that went into creating English didn't split infinitives because they couldn't: they were single words. English is more flexible. Flex it.
Since this is a useful word in both storytelling and explicating situations, and since it's so abused throughout politics and popular culture, every misuse of this word should be pounced on with furious indignation and condescension.