It seems there is some controversy on this thread as to who is a Muslim and who isn't, and I've seen some people say that by marrying a Hindu or a Sikh a Muslim becomes a non-Muslim.
If someone believes that there is only one God worthy of worship, that He has no partners, and that Muhammad (SAWS) is His last and final messenger, then they are Muslim. You cannot call this person a non-Muslim unless they deny this, or they deny a fundamental aspect of Islam like Salah (Namaz).
If a person believes this, but he drinks alcohol, has sex outside of marriage, and doesn't pray, he is a sinner, but still a Muslim. If he says that Salah/Namaz is not required - that would make him non-Muslim. But if he believes in Namaz but just doesn't do it, it doesn't make him non-Muslim, just a very bad and sinning one.
Furthermore, the idea of Asabiyyah (originally "tribalism" but now also meaning "nationalism"), which means blind loyalty to your tribe, country, etc, is foreign to Islam. If someone practices it, they are being a bad Muslim, not a non-Muslim. You shouldn't place your country or your tribe, like Pakistan, India, or US, or whatever, before Islam.
I support Pakistan as an Islamic country, as a homeland for the Muslims of northwestern South Asia, and I call myself a Pakistani because the ideals for Pakistan go hand-in-hand with those of Islam. Where the actions of Pakistan's government, Pakistan's military, and the Pakistani people are anti-Islam, I openly criticize and oppose them and seek to change them.
My primary loyalty lies with the principles of Islam, and Islam sees no borders based on ethnicity, race, or politics. In the end, Pakistan for me is just one step up in the ladder from colonial rule to re-establishing the Khilafat. The Ummah was under colonial rule. Now we are free and rule ourselves and can start rebuilding. Then we can start uniting, for example, Pakistan-Afghanistan-Iran, and so on and so forth until the whole Ummah is one State. I don't see Pakistan as an independent state forever. I see Pakistan as having been founded for the purpose of uniting itself with Muslim and Islamic states elsewhere in the world. Eventually, all these Islamic states merge together as the provinces of one Ummah State.
As far as Indian Muslims go, Pakistan today cannot be called an Islamic state so I don't think they should feel an obligation to make "Hijrat" to Pakistan. But at the same time, as Muslims, they should not be caught up in blind nationalism ("Asabiyyah") and should forge brotherly ties with Muslims all around the world, including in Pakistan. Pakistanis, on the other hand, should work towards making Pakistan an Islamic state that can be the Noor of the Ummah and an example for all nations to imitate, both Muslims and non-Muslims.
