In the worksheets provided by this site, this answer is marked a mistake too.
Could you please point me to those worksheets, Heidita?
But in any case, I was thinking about the
"I would have came" part.
My argument is, if we accept
anything in language and don't follow any kind of rules or directions,
anything could be said, and nothing would be considered a mistake or "wrong English".
But we don't just accept anything in language, Heidita. For speech, which is a different ballgame to the written language, ENLs follow the rules of their dialect fastidiously.
You're confusing prescriptive rules with the actual rules that govern how we use language.
Read this. It'll help you to understand the difference between prescriptions and the real rules of English.
http://pinker.wjh.harvard.edu/articles/media/1994_01_24_thenewrepublic.html
I wonder...in Spain there is the Royal Academy which sets the rules. I know in English there is no such Academy but I believe that not everything can be accepted just because it is "said".
In that same article, above, there is this:
Someone, somewhere, must be making decisions about "correct English" for the rest of us. Who? There is no English Language Academy, and this is just as well; the purpose of the Acade'mie Francaise is to amuse journalists from other countries with bitterly-argued decisions that the French gaily ignore.
Nor was there any English Language Constitutional Conference at the beginning of time. The legislators of "correct English," in fact, are an informal network of copy-editors, dictionary usage panelists, style manual writers, English teachers, essayists, and pundits. Their authority, they claim, comes from their dedication to implementing standards that have served the language well in the past, especially in the prose of its finest writers, and that maximize its clarity, logic, consistency, elegance, precision, stability, and expressive range.
William Safire, who writes the weekly column "On Language" for the [New York Times Magazine], calls himself a "language maven," from the Yiddish word meaning expert, and this gives us a convenient label for the entire group.
To whom I say: Maven, shmaven! [Kibbitzers] and [nudniks] is more like it. For here are the remarkable facts. Most of the prescriptive rules of the language mavens make no sense on any level. They are bits of folklore that originated for screwball reasons several hundred years ago and have perpetuated themselves ever since.
For as long as they have existed, speakers have flouted them, spawning identical plaints about the imminent decline of the language century after century. All the best writers in English have been among the flagrant flouters.
The rules conform neither to logic nor tradition, and if they were ever followed they would force writers into fuzzy, clumsy, wordy, ambiguous, incomprehensible prose, in which certain thoughts are not expressible at all. Indeed, most of the "ignorant errors" these rules are supposed to correct display an elegant logic and an acute sensitivity to the grammatical texture of the language, to which the mavens are oblivious.