Pakistan was created in a particular context when the British colonial rule ended over the Indian subcontinent and it became clearer that majority Hindus would dominate the Muslims and force them to assimilate within Indian Hindu culture which is considered disgusting and crass to say the least. Some pictures of Hindu culture:
We would have had to call these our countrymen and been forced to assimilate with that hideous Hindu culture of theirs. Sorry but our Islamic culture is more dear to us and accepting secularism would have meant us mixing with these hideous people. Can't accept secularism in a Hindu dominated culture.
I am Pashtun from KPK. My forefathers were classified as Indian Muslims during British rule and we were always quite close culturally to Indian Muslims whether it be Punjabi, Bihari, Kashmiri or whatever. They followed Islamic culture and abstained from assimilating withing Hindu society. Naturally Indian Muslims of that time wanted a country of their own free from Hindu culture and practices. And voila, we got Pakistan thanks to Allah swt.
I am a Muslim and I don't have any problem assimilating with Christian or Jewish or Parsi societies. But Hindu culture is something I would stay miles away from. Sorry if I am being racist here. I can't stand Hindu culture. Its quite unhygienic and dirty. So its quite justified that we sought a separate country.
To answer your last point, there are over 800 Afghan refugee families in Jalozai where I am from. So its not true what you said. The war in Afghanistan is pretty much over now and the country is relatively stable so its time for them to go. The Burmese Muslims are stateless people within their own country so its imperative to support them for humanitarian causes just like we helped the Afghans out.
If Muslims all over the world can have their own land, why can't we and especially one where we don't have to tolerate Hindu culture.