The presumption that had India not been partitioned, the population of muslims in an undivided subcontinent would have been the same as the sum of muslim populations of the three divided nations, is wrong. A majority of Pakistan wasn't Muslim when it was created. Punjab was more Punjabi than Muslim. Sindh was more Sindhi than Muslim. These states became systematically Islamized after the conservative policies of successive administrations. By allowing them to create a separate Muslim nation we allowed them to populate that erstwhile non-Muslim region with Islamists. These same people are trying to hurt India from the outside now.
Their head snake, Jinnah himself was an Ismaili (later converted to Shia), would be an illegal in Pakistan today. Why? that's because Pakistan later declared Ismailis to be non-muslims. Anyway, had India not been partitioned, the population of muslims in the subcontinent wouldn't have been what it is today. So calling it 'good riddance' is like kicking off our own premium real estate for the sake of a few muslim elites. When the partition was done, even the soft spoken Sindhis in Sindh started complaining that an influx of foreign muslims (snakes from Uttar Pradesh aka Mohajirs) was being imposed on them. Sindh today has lost its Sindhi character as a direct consequence of partition. Basically we let a few people who were hostile to Hindus, migrate to a separate country whose geography was relatively larger than the size of the migrating population, and allowed them colonize it through large scale Sunni breading over the decades.
Also note that these elites were all Shias. I thought I'd add that since we are on a Shia-Sunni thread. Many of Pakistan’s leaders were Shias, including one the country’s first governor-generals, three of its first prime ministers, two of its military leaders like general Iskandar Mirza and Yahya Khan, and many other prominent people. It was *made* a Sunni state by conscious foresight.
Also, we lose more than just land. We lose the birthplace of our Hindu roots, that is the Sindhu river and the Sindh valley. That is where we derive the word Hindu from (and the English name 'India' is derived from Indus). Whoever conceptualized the partition clearly did so keeping in mind that all symbols of Hindu cultural pride stayed outside of the new India so that the people lose their sense of identity and pride and source of heritage.
About Bangladesh, well, they took a chunk of land but they are still hopping over fences and migrating to India. 1/3 of Bangladeshi population lives in India now, does that mean that we get to annex 1/3 land of Bangladesh as compensation? No. That land is gone forever. That's the problem. the loss of land is permanent, but the loss of snakes is temporary. Once the new nation is created they still continue to invade and migrate to the parent nation and then they will ask for more. Therefore one should be so elated at the prospect of giving away land. Take notes about how Myanmar has handled it's Rohingya separatism with an iron fist. That's how a nation upholds its self interest. Lets not pat ouerselves on the back for proudly throwing away large swathes of land full of resources. (There's massive oil reserves in Bangladesh and Baluchistan.)
Also, Mansarovar has gone to China, and Amarnath has gone to a hostile state of Kashmir. We have lost control over our 3 most holy sites Ayodhya, Mathura, Kashi. We have lost ALL control over all temples , their revenue and administration in India to the government, unlike the snakes who have their autonomous Wakf board. So please don't sound so happy when you say 'good riddance'. Of course, I don't want the partition to be undone now; Adding more toxic people into our nation is the last thing anyone wants, but please be nuanced with your approach. I take as much pleasure as you do, in heaving a sigh of relief that a lot of snakes were booted out during 1947, but such a statement must always be followed by a disclaimer about the corresponding loss of land and heritage sites, which is not a good thing. Unfortunately we Hindus have no appreciation for history. The partition was as bad to us as the holocaust was to the Jews. The Jews make movies about it, write books about it, and pass on the heritage to their generations. And we Hindus say 'good riddance'. It's good that we rid ourselves of poisonous people but the fact that it came at the cost of our land and heritage is a painful lesson we must not brush off. Look at Israel which has expanded its territory after every war with the Arabs and look at us, giving away concessions despite winning every war.
Undoing partition now might be a bad thing but that doesn't imply by corollary that partitioning the nation back then was a good thing. Let's not throw the baby away with the water.
Tagging
@maomao @Srinivas_K @asingh10 for their thoughts on this.