A large part of the Hindutva ideology's energies are devoted to denying the two-race theory in all its forms. [While the Aryan Invasion Theory may or may not be valid in its literal form, there is enough genetic evidence that North Indians and South Indians differ significantly in the proportions of the genes they inherit from two distinct genetic groups.]
It's therefore amusing to hear a North Indian admit, however inadvertently, that South Indians are a distinct racial group ("black people", in his words). BJP MP Tarun Vijay's interview to Al Jazeera, where he sought to deny the racism of Indians against Africans by using an unfortunate example of "black people" (South Indians) within India, has sent shock waves through the country.
To my mind, the root of Hindi language chauvinism comes from this inherent sense of superiority. If North Indians truly respected South Indians, there would be a more sincere attempt to implement the three-language formula, in place of the current lopsided emphasis (budgetary and otherwise) on the propagation of Hindi at the expense of every other Indian language.
Clearly, North is North, and South is South, but if the twain are to live amicably together in one country, mutual respect is a non-negotiable condition.