The mavens’ case about case rests on one assumption: if an entire conjunction phrase has a grammatical feature like subject case, every word inside that phrase has to have that grammatical feature, too. But that is just false.
Jennifer is singular; you say Jennifer is, not Jennifer are. The pronoun She is singular; you say She is, not She are. But the conjunction She and Jennifer is not singular, it’s plural; you say She and Jennifer are, not She and Jennifer is. So a conjunction can have a different grammatical number from the pronouns inside it. Why, then, must it have the same grammatical case as the pronouns inside it? The answer is that it need not. A conjunction is just not grammatically equivalent to any of its parts. If John and Marsha met, it does not mean that John met and that Marsha met. If voters give Clinton and Gore a chance, they are not giving Gore his own chance, added on to the chance they are giving Clinton; they are giving the entire ticket a chance. So just because Al Gore and I is an object that requires object case, it does not mean that I is an object that requires object case.
I find Pinker's reasoning utterly wrongheaded in this. It flies in the face of a commonsense notion that, in the case of a compound object, each element of the compound carries the same (objective) case. I wonder whether Pinker himself actually takes the above reasoning seriously. Does he write "between you and I" in his research papers? Does he bow to whatever style manual (probably APA) governs the writing of those papers? If he does bow to convention, then why does he do so? That, too, would be an interesting subject to explore.