muslas is no word ,word is muslim similarly paki is no word ,word is pakistani.It is not the word but the connotation of the word. In England if you call a Pakistani a Paki, you can goto jail for racist behavior but we Pakistanis use the term as a short form and it doesnt mean anything to us. The word 'kafir' is equivalent of 'musla' in India. How do you think Indian Muslims feel when they are called Muslas by the Indian 'Kafirs'?
kafir is equal to non believers so why you have so much problem with it.