The key paragraph in the argument for our purposes (i.e., with South Asia in mind) might be the following:
In the 19th century, there was a memorable debate between John Stuart Mill and Lord Acton. John Stuart Mill had argued, in a text that was to become the bible for separatists all over, including Jinnah and Savarkar, that democracy functions best in a mono-ethnic societies. Lord Acton had replied that a consequence of this belief would be bloodletting and migration on an unprecedented scale; it was more important to secure liberal protections than link ethnicity to democracy. It was this link that Woodrow Wilson elevated to a simple-minded defence of self-determination. The result, as Mann demonstrated with great empirical rigour, was that European nation states, 150 years later, were far more ethnically homogenous than they were in the 19th century; most EU countries were more than 85 per cent mono-ethnic. (link)
In his Column in Indian Express, Mehta keeps his focus sharply on Kosovo's status within Europe, and also considers the seeming double standard as the Western powers disregard Russian objections to Kosovo's independence, on the one hand, while they go out of their way to accommodate China's (unconscionable) policy on Taiwan, on the other.
But there is obviously a question for South Asia here as well, and India in particular. Mehta briefly alludes to the history of nationalism in the Indian subcontinent when he invokes Jinnah and Savarkar, but his column raises questions for us as we think about the present too -- specifically the questions over the status of Kashmir and Assam (maybe also Manipur and Nagaland, not to mention Punjab in the 1980s).
The debate between Acton and Mill Mehta invokes isn't so much a "conservative" versus "liberal" debate -- John Stuart Mill is considered one of the architects of the philosophy of liberalism, but in this case his views come out as less "liberal" than Acton's. Mill supports thinking of nations as defined by race/ethnicity, but that approach can reinforce ethno-religious differences, rather than leading to an environment where different communities have equal status in a diverse nation. I tend to favor Acton's approach, except perhaps in cases where minority communities face imminent violence, or genocidal suppression.
(Incidentally, Mehta builds his arguments on an essay called "The Dark Side of Democracy" in New Left Review, by Michael Mann; for those who have subscriptions, you can find the article here.)