Ganesh Devy isn't the only one with those views; they're pretty common among linguists. Perhaps because linguists know that language gives you a sense of belonging, connecting you to your peers, and to erase the language of a people is the same as to erase that people. Or, let's be blunt: like @Nakoichi@hexbear.net said, it's genocide.

That gets specially obvious if you rephrase the question in the title as "Should a government destroy that sense of belonging and the cultural diversity of the peoples subjected to the government, for the sake of some nationalistic babble like «cultural unity»?" (For any decent and morally sane person, the answer is "no". )

Language could liberate, but it could also disintegrate [...]

How's Switzerland going? There are language struggles there, such as the Romansch varieties slowly dying out, but you don't typically see independence movements there gaining any sort of traction; not even among the Gallo-Romance speakers, even if they would be backed up by some rather powerful nextdoor government. "Perhaps" because Switzerland doesn't treat its citizens as second class based on language?

In other words, because the government of Switzerland does the opposite as the government of India is trying to?