I share your concern about Islam. The qualifications for being a Christian are objective and not subjective. It is not that I decide who are Christians and those who are not. Those qualifications have been established nearly 2000 years ago. Which is more serious, being killed by a terrorist or losing your salvation? Anyone that believes what Mormonism believe about God is eternally lost.
So, what you are saying is that if I don't care whether Mormons think they are Christians or not, I will not be saved? Funny, I don't remember seeing that in the Bible, but I'll ask my preacher.