"Would of", "could of", "should of" are certainly errors when conjugating , but "on accident"? Either preposition "by" or "on" seems correct to me and the correct choice seems arbitrary -- though I find myself preferring "on".
From what I could find doing some (brief) research, this is a case in which the difference breaks down nearly perfectly along generational lines. Those ages thirty-five and under overwhelmingly prefer "on" and those younger prefer "by"[1]. Prepositional choice has always seemed a bit arbitrary to me, and the fact that there are dialectical differences reenforces that belief[2].
To suggest that this contributes to a "generation holding the less weel read attitude that grammar doesn't matter" strikes me as a bit misguided.
I chose "on accident" precisely to inject the generational notion into my comment, being well aware of its notability as an indicator of usage patterns by age.
First, in your citation 1, you have the generational aspect of "on" and "by" reversed. The original and correct[1] usage is "by accident". Acceptance by the younger generation doesn't make "on accident" correct, it is just accepted for lack of knowing otherwise. (This will, granted, eventually result it in showing up in dictionaries as a usage.)
The new generation, whether less read or less likely to have read the writings of prior generations, is less influenced by existing usage, and mistakenly verbalizes "on accident" to over-regularize with "on purpose".
"Over-regularization" is the kind of mistake a toddler makes until they learn correct usage by hearing and reading correct usages from multiple example experiences.[1] As the new generation reads less old material, and socializes textually with peers more and earlier, incorrect usages imprint to the point they gain defenders from the "everyone's doing it so don't call it wrong" camp.
I'm not making an argument ad populum and even if I were, I don't see how it holds any more weight than your argument from antiquity.
Language and grammar evolves and as far as linguistic changes go, the use of one preposition over another is pretty benign. Prepositional choice is already essentially arbitrary and varies from region to region.
English is a moving target. The current generation forming its own vernacular doesn't make in any more or less correct than when the previous generation did it. It's not as if English has its own académie française, and the flexibility of English is one of its most charming properties.
Leaving aside the condescending quip about toddlers, I don't see how over-regularization of prepositions is a bad thing. They're already confusing enough as it is and I personally would prefer a language with more consistent rules than not.
EDIT: A quick addendum: I didn't actually know this was a mistake and I appreciate having learned it anyway.
I was referencing toddlers and how that age group learns. The word toddlers is not condescending, it's simply the most appropriate word for the age group in question.
> I don't see how it holds any more weight than your argument from antiquity
The dictionary is nothing but "argument from antiquity", as would be the conventional definition of "correct usage", in contrast to the "many people doing it wrong makes it right!" definition you disavowed, skipped a graph, then repeated.
Prepositions are not "essentially arbitrary" even when used with metaphysical concepts. Particular prepositions work with particular types of concepts, and curiously, end up quite similarly used among a variety of cultures and languages. In English, for example, is the concept something you can possess, or a process that happens to you? If you consider other things that couple with "on" or "by", you'll see what I mean.
Certainly English is charming, and rapidly evolving. You've likely read Bill Bryson's "The Mother Tongue", but if not, you might enjoy it.
From what I could find doing some (brief) research, this is a case in which the difference breaks down nearly perfectly along generational lines. Those ages thirty-five and under overwhelmingly prefer "on" and those younger prefer "by"[1]. Prepositional choice has always seemed a bit arbitrary to me, and the fact that there are dialectical differences reenforces that belief[2].
To suggest that this contributes to a "generation holding the less weel read attitude that grammar doesn't matter" strikes me as a bit misguided.
[1] http://www.inst.at/trans/16Nr/01_4/barratt16.htm [2] http://en.wikipedia.org/wiki/American_and_British_English_di...