Let's say the KKK committed some horrible atrocity in a country (let's call it Grillo) where there aren't many Christians. Previous to that atrocity, most people in Grillo either knew nothing about Christians or had a vague sense of distrust about Christians, partly because they only ever hear about Radical Christianists (which is what people in Grillo call the type of people who are associated with the KKK). There are very few Christians in Grillo. When the Radical Christianists/KKK commit that evil act, everyone in Grillo thinks there is a connection with the Christians living there. The Christians there say they have nothing to do with the KKK/Radical Christianists (it's never even occurred to them that anyone would connect them with violent radicals like that) and condemn the violence, just like everyone else in Grillo does. But for years afterward everyone in Grillo keeps telling the Christians they have to do something about the KKK/Radical Christians because there must be something wrong with Christianity to produce radical Christianists, or that the religion is backward and it needs to make major changes so that Radical Christianists will disappear.
This is obviously hasn't really happened anywhere, but it illustrates why I get frustrated when people ask why Muslims aren't stopping violence that is committed in the name of Islam, or at least speaking out against it. Leaving aside the fact that many Muslims do speak out against it (even if you don't see that on the news), I don't want to put the responsibility for finding a way to stop extremists on moderate Muslims any more than I feel any responsibility to stop the KKK. The KKK may say they're Christian and following Biblical principles, but their ideas are so far from my reality that I feel absolutely no connection to them.