There's only one way to settle the question. What does the Qur'an and other texts considered sacred by Muslims say about the value of human life outside of the faith? It doesn't matter what other people claim Islam represents to them. If I want to know what Catholicism means, I don't find some random Catholics and ask them, taking their often contradictory opinions to be the "supreme authority." I look at the Catholic Bible and the statements of the Popes, as that religion is defined by what they believe to be God's words. Islam is a religion of the book. In other words, it is defined by their sacred texts. "But what about interpretation?" you might say. Sure, it is important to see how Muslim scholars have traditionally understood the words. In this I also see no inconsistency between Mohammad's biography, the sacred writings of Islam, and some of the most brutal actions of ISIS. The moderate Muslims are the people who reject the first two, disregarding the notion of their righteousness and perfection, so that they are able to clearly and emphatically argue against the latter as being neither righteous nor perfect as well.
He who loves God cannot endeavour that God should love him in return - Baruch Spinoza
