How would I end Muslim extremism? Well, I can at the very least say that your suggestion, which would be the largest genocide in history, is not the answer. But the question of "how would YOU stop Muslim extremism?" or any kind of religious terrorism, is essentially an impossible one. It's like asking someone how they would end something like mental illness, world poverty, or war. It's not something that can be solved by a single leader or nation, and it has no, so to speak, "final solution." However, where religious extremism is at its minimum is in politically stable nations, with governments that are secular regardless of the religious majority, and allow freedom of speech and press. Part of the prevalence of religious terrorism stems from the potential political divisiveness of religion's indoctrinating capabilities. If you have a government that is claimed to rule by divine mandate, and be endowed with the privilege to interpret the will of God, then you run into all sorts of problems. It's like The Crusades; the people who ran the show mostly did it for political or fiscal reasons, whereas the majority who did the dirty work massacred tens of thousands of people because they were taught that it was the will of God. Additionally, anyone who opposed it was condemned and potentially punished. Such oppression of free speech is also why the Muslim majority in many Islamic theocracies who vehemently oppose their violent regimes do not speak against them; they are forced into silence.