The reason why "good muslims" do not try to stop/denounce "terrorist muslims" is:
1. Quran approves of and endorses "terrorist muslims"
2. Good muslims might get decapitated by terrorist muslims for speaking out.
3. There is no such thing as a "good muslim", there is only "good people" who happen to be muslim.
These good muslim are ignorant of what Mohammad teaches and did in his lifetime. Even though it is all written in their holy texts. The raping, pillaging, highway-robbery, assassinations, etc.
These terrorist are simply following the sunnah.