I have gotten into heated debates about this very topic, so I have no grounds to begrudge the hordes of online anal retentives who compulsively need to correct everyone else's mistakes. All the time. Everywhere.
Maybe this is a weird stance to take from a guy who purports to edit things in his non-professional capacity as an editor of PDFs, but I don't assert my opinion here out of personal convenience.
The idea that languages -- in this case we're going to talk about English, but what follows applies to ALL living languages that aren't Klingon or Sindarin or otherwise invented by nerds as a kind of intellectual exercise and/or artform --
The idea that languages have static rules and possess an inherent proper form is bunk and can only be construed as non-bunk in the sense that there is a tacit social agreement among societies that this must be so. Artificial rules of language begin to be indoctrinated into English-speaking humans shortly after birth with the expectation that everyone will be on the same page by the time they reach maturity.
Like how we're on the same page regarding AIN'T.
We will all know that ain't isn't a word.
And yet, AIN'T has form (note the letters and symbol that make it up) and meaning. We are all secretly aware that it makes a fine substitute for ISN'T in the sense that it conveys the same relationship equally well, and yet some of us hate AIN'T for the sole reason that it isn't proper.
What a bunch of cunts.
"Proper" loses its meaning very quickly as we back away from the timeline of History and actually consider how much "Proper English" changes, mutates, absorbs, adapts, devolves, evolves in relatively short periods of time. People did not stop speaking Middle English because some advanced linguist discovered Modern English and everyone agreed that it was better. The very boundary between Middle and Modern is a blur of linguistic indistinctness.
The notion of Proper English itself isn't all that very old.
The point here is that language never stops changing, and notions of Proper English erode and partially collapse continuously.
Bitching about it is like bitching about the weather.