Something a lot of people don't think about, too, is the racism and classism inherent in some of these statements. You can't just assume that someone has had the same educational opportunities as you have, whether because they couldn't afford them, or because they were never even available.
And who decides what grammar is, anyway? The vast majority of our spelling and grammar bibles were written some time ago by old white men. I see people on the internet bashing AAVE all the time, for example, calling it "bad English" when in actuality it's a legitimate dialect of English, with grammatical rules of its own that are just as stringent as the rules of so-called "standard" English.
Let's be clear, I'm not accusing you of being racist or classist. I'm trying to point out these two, in my opinion very salient, points. I've had to learn that yes, I know the difference between to and too - but that I was lucky enough to a) have someone teach that to me, and b) be able to comprehend and retain it.
I'm not perfect either. There are certain linguistic foibles that bug the heck out of me, but I do my best to keep the previous thought in mind: that just because I know (and care) what that person spelled/wrote incorrectly, doesn't mean that person knows (or cares).
Language is about conveying a thought from your head into another person's head, whether by actions or by language, written or spoken. Language is an entirely arbitrary system of sounds we at one point chose to represent concepts. I think as long as you have successfully conveyed your thought to someone else, then you have successfully "languaged", so to speak, and everything else is just window dressing.