[quote=@Vilageidiotx]
If a mistake is so commonly made, it means that the distinction no longer has a meaningful function. Your/You're can (and just very well might) melt into a single word and it will not harm the language in any way. Your just being pedantic.
[/quote]

I just outlined a valid example of a way in which such a change [i]would[/i] harm the language. 'You're' and 'Your' have entirely different meanings, both of which can make sense in context and convey two entirely dissimilar messages. Any fundamental change to English grammar would introduce ambiguity. It is for the sake of maximizing the English language's purpose, as a medium of communication, that I correct grammatical mistakes. Stuffiness doesn't factor into it.

If you want an example of a grammatical rule that IS entirely unhelpful in maximizing communication, go find a grizzled old grammarian who insists that sentences shouldn't end in prepositions.