I also think you're on to something, Catching, about it being disrespectful. It's one thing to make occasional mistakes. It's another to consistently use bad grammar, or even worse, ignore a correction and continue to spell or misuse a word incorrectly. It's like waving that you don't care in someone's face.
It also amazes me, like Norad mentioned, how many things I read that are for an audience that aren't proof read, such as minutes, news articles, etc. It's pathetic.
Regardless of my opinion, I will never understand how so many people want English as the only language, when they refuse to use it correctly themselves!