Why aren't the Indians more grateful?

[Mr Greene]

Personally I find that anyone who attempts to describe European colonialism as either good or bad invariably knows **** all about it.

I would be hard pressed to find anything good on European colonialism. Other than serving their home country that is.

They set up a chain of monocultural economies that didn't serve the place when they finally got independence. What's more, they weren't interested in ethnic integrity of the region, which led to many civil wars over who's ruling whom after colonial rule was over. It also prevented all these regions from finding their own identity and an equal role in the global economy.

There have been worse and better colonial regimes. The Belgian king's rule over the Kongo probably one of the worst, but that doesn't mean that any colonial rule ever cared over the wellbeing of the indigenous people there.

At the start, they were sold of into slavery and at the end they were exploited to serve the need of the motherland in question.

So, no. You can't say, colonial rule provided much of a benefit to the people in the colonies. Only for the motherland, in terms of trade goods and global influence.

Apart from the development of global trade to take part in, the dissemination of ideas and culture across the planet in all directions, the development of hybrid cultures and scientific knowledge, etc. etc. etc. 
Or is Singapore still an uninhabited mangrove swamp? Do Indian and Chinese goods not pass your threshold? Do we not have morphine, telephones, the theory of Evolution? 
The thing about globalization is that everyone on the globe benefits from it.
Except perhaps Nationalists who find the benefits inconvenient for their preferred narrative.