1) it is the only Muslim majority state within India
And there are other states where minority is majority.
2) It borders Pakistan and they identify ethnically and culturally more with Pakistanis than with most Indians
By that logic, we can claim whole of Pakistan.
3) the whole history of how they were forced to be with India, Hari Singh's signature does not mean anything
How ironic, that signature does not mean anything yet India will keep Kashmir forever because of that simple stroke of pen.
4) lastly, they are backed by Pakistan of course which gives them the courage to fight
They r most welcome to fight but then should be ready for the result. We told the same thing to "their source of courage" in 1971 who was even more inclined to fight.
Given a choice, I'd say that most Muslims except extremely assimilated ones (which don't qualify as Muslim) would want a separate Muslim state as it is supported in their religion.
Given a choice, I would like to declare my estate in Haryana as an independent country but that is not how the real world works.