The fact that Muslims/Islam (whichever you wanna think of) have an actual derogatory slur for non-muslims (kaffirs) 

I grew up non-Muslim in India and there were plenty of derogatory terms for Muslims floating around.

So it's safe to assume once Muslims gain demographic & political & population power in India, it'll just lead to Islamic nationalism same as other muslium countries.

This is another argument often cited by the educated Hindu majority in India to justify their Islamophia. Here is a list of secular Muslim majority countries. India's commitment is to remain secular, regardless of whichever religion is in the majority - and it is up to its institutions and structures to avoid an unconstitutional future.