Grammar is many things packed in one. For one, it can signal a bunch of things, like maturity, superficiality, seriousness, intelligence. The lack of tolerance,

Grammar is many things packed in one. For one, it can signal a bunch of things, like maturity, superficiality, seriousness, intelligence. The lack of tolerance, like in you're example, is likely just someone who wants to vent, not a genuine concern for grammar. The other thing is that writing on the open internet means that potentially many people will read the writing. Good grammar is borne out of routine, but this only works if the people practice the right thing - if they practice the wrong thing, then next time they'll potentially do the wrong thing by habit. So really, good grammar depends on reading texts with good grammar. It's also how we pick up vocabulary. Putting these things together, I think people owe it to each other, and the collective humanity, that they produce quality writings on public places.