What you are calling "Islamic extremist ideology" isn't extremist. He was simply following the teachings of the Koran and Hadith, and the example of Islam's perfect man, Mohammed.
To quote from the Koran:
Surah 2:191: And kill them [non-Muslims] wherever you find them
Surah 9:5: Then kill the disbelievers [non-Muslims] wherever you find them, capture them and besiege them, and lie in wait for them in each and every ambush
Of course, apologists for Islam will say that these verses are taken out of context. But then, that's apparently what Moslems do to justify their violence to Christians and to Jews.