I still wonder why it's called snobbery to believe that language should have standards. But more so I wonder how I became a grammar snob, given that my own education in the subject was so bad. One year we learned about nouns and verbs, the next about Class 1 and Class 2 words, then something else, as educational fashions changed—and then I think the teachers just gave up. So nearly all I know about grammar came from French class, from reading good books, and from listening to my parents, who spoke well themselves. I still can't explain why something is right, but for the most part I know it when I hear it.
Come to think of it, maybe that's actually why I care about good grammar: if what we read and what we hear can no longer be counted on to help us intuit the rules of a language, what is to become of those whose schools fail them?
And on the point of the comic, school failed us almost at once. I can't imagine that "on accident" was actively taught, but I do know that Heather had not been in a school environment very long before the phrase became cemented in her vocabulary, so I doubt much effort was put into correcting it. Then again, maybe the teachers tried—but peer influence is so terribly strong. Certainly I tried. But as I said, I may (usually) know what's right when it comes to the English language, but I still lack the tools to be persuasive about it.
Anyway, this comic made me smile, because it gibes both ways.