He's an expert on language or something. The logical implications of their position can be made evident. An alternative tack, then, is to agree with them, and excoriate them for only now waking up to the degradation of language. Loss of the case endings has been going on for a long time, let's bring back nominal as well as pronominal inflection, genitive and dative at the very least. But they are like the deaf nadder that stoppeth her ear.
Nobody actually uses it.
People seem to pick up languages perfectly without resorting to abstract analyses, and those who do resort to them don't necessarily learn them better or faster. At the secondary school level, people don't care about deep structures or sense relations or segmental or suprasegmental properties of sounds, they just want to learn general, basic, useful things that will be of use whatever they choose to do later in life. And linguistics, sorry to say, isn't one of these useful things, at least not at the moment. Mike Maxwell suggests that one problem with getting linguistics widely accepted is that we require the same prescriptivism that everybody else does within our journals. One conundrum about studying human behavior is that the studiers must of necessity also be participants.