A language is defined in terms of how it is used, but a language is not supposed to be used in the way it was defined, if so, we'd still be speaking proto-indo-european, or maybe we'd never be able to speak, as there wouldn't exist any grammar before a language existed. So, being a grammar nazi is plain stupid.
Be charitable. If you haven't been exposed to actual linguistics (and know about things like PIE), you have the current, normal, common-sense view on language, which is that what you speak is normal, and what speakers of any other dialect or language do it wrong. I've heard intelligent, university educated people say things like "I don't want to learn $Language with an accent". The fact that no such 'accent-less' language exists is simply not a fact that they know. Such misconceptions about, and people who suffer under them are misguided, not stupid.
Misconceptions do not matter here. One may have misconceptions, but this does not justify correcting people for their grammatical errors on a thread that has nothing to do with grammar or whatsoever and thus hijacking it. It should be obvious that a serious lot of people here are not native-speakers.
