From his conclusion:
At the end of the day, language death is, ironically, a symptom of people coming together. Globalization means hitherto isolated peoples migrating and sharing space. For them to do so and still maintain distinct languages across generations happens only amidst unusually tenacious self-isolation—such as that of the Amish—or brutal segregation. (Jews did not speak Yiddish in order to revel in their diversity but because they lived in an apartheid society.) Crucially, it is black Americans, the Americans whose English is most distinct from that of the mainstream, who are the ones most likely to live separately from whites geographically and spiritually.
The alternative, it would seem, is indigenous groups left to live in isolation—complete with the maltreatment of women and lack of access to modern medicine and technology typical of such societies. Few could countenance this as morally justified, and attempts to find some happy medium in such cases are frustrated by the simple fact that such peoples, upon exposure to the West, tend to seek membership in it.
What McWhorter doesn't talk about, though, is the fact that language death is also, historically, associated with conquest and exploitation. As nations dominated indigenous peoples in the lands they colonized, they also sought to wipe out the languages of those peoples. In Ireland, for instance. Or the United States.
Did the Native Americans and the Irish tend to seek membership in the cultures that took over their lands? Was such membership allowed or encouraged? Did the arrival of the British and the Europeans bring the wonders of modern medicine and technology and enlightened gender relations? Are things really so much better today?