Like ADCMS implied, the people who live literally by the Bible rules are the worst of all. This includes the Quran, which is a spin-off of the Old Testament.
People like Boco Haram, ISIS and Taliban, who slaughter others on the basis of faith, who treat women like domestic cattle (or worse), all those people are people who live literally by their holy book. It is misleading to call them religious extremists: They just DO literally what their Book says. As a matter of fact, the moderate religious people are more hypocrites, since they cherry-pick whichever passages of the Holy Book make them feel comfortable (or are allowed by the law) to follow.
Not to leave Christians outside of this: The Amish and the JWs are examples of people who follow lots of their Bible instructions literally, and genarally are worse than the average secular person. Worse in an ethical sense (shunning, forbidding of normal sexual activity, blood etc.)
The only reason Christians like JW and Amish don't do 100% literally what their Bible says, e.g. killing apostates instead of shunning them, is because the Law of their countries forbids it. When the secular law allowed it (from 400 AD to to almost 1800) they did it, and they did it plentifully (remember the witch trials, not of the Dark Ages, but of the New World in 1600 and 1700s). The Islamists still do it (the killing) because their theocratic states still allow them to.