Actually, what people like Obama, Paul, Volsky, and Jenkins consider “true” faith is this: “faith that promotes the kind of behavior that I like.” So, as do all believers, the apologists pick and choose from scripture the dictates that they find congenial, ignoring the bad ones.
Many beliefs of some Muslim sects—like female genital mutilation and devaluating a woman’s testimony in court (according to sharia law, it’s worth only half of a man’s) —are not explicitly given in the Qur’an, the word of Allah supposedly dictated to Muhammad. Rather, they have become associated with Islam through the hadith and the sunnah (reported sayings, practices, and beliefs of Muhammad), or through simple tradition. ISIS has an extreme and fundamentalist interpretation of Muslim doctrine. But in exactly the same way, dogma about the immorality of abortion, homosexuality, premarital sex, and divorce have become part of Catholicism. They are theological interpretations of scripture that appeal to some people’s sense of morality. Others disagree. Whose faith is “truer”?
In the end, there is no “true” religion in the factual sense, for there is no good evidence supporting their claims to truth. Nor are there “true” religions in the moral sense. Every faith justifies itself and its practices by appeal to authority, revelation, and dogma. There are just some religions we like better than others because of their practical consequences. If that’s what we mean by “true,” we should just admit it. There’s no shame in that, for it’s certainly the case that societies based on some religions are more dysfunctional than others. Morality itself is neither objectively true nor false, but at bottom rests on subjective preferences: the “oughts” that come from what we see as the consequences of behaving one way versus another.