Now give me an example of a country as diverse and massive as India whose lingual diversity was a hindrance to growth. I will just go ahead and respond. There is none. India is unique and there is no evidence it's current model won't work.
Languages evolve all the time> Incorrect. Languages evolve over centuries due to several geopolitical reasons like: land topography, availability of food, neighboring tribes. Each language and it's multiple dialects are an imprint of the struggle their speakers went through over hundreds or thousands of years. In case of India, the frequency is so high since it has been a melting pot of the world for a very large period of time.
>Global society Contrary to what you believe it's not synonymous with a central society. The ultimate goal of the human race is a moving target. Adopting a common language so that we can do better trade, better science and produce more is fallacious since we don't know that's we are supposed to do. Maybe we need to slow down so that we don't kill ourselves off by becoming too powerful and cocky. I don't know. Neither do you.
Languages evolve all the time. If everyone were to hang on to the languages and identities that were present and predominant at the end of the twentieth century, I don't think we'd get anywhere closer to a more global society. As a nation, there's much more of a reason to have a common language.