How does a Religious Radical become Dangerously Extreme?

Both Christianity and Islam have dangerous radical elements. Buddhism, though not technically a religion, has a few radicals as well (remember the self immolation by Monks during the Vietnam War and the war with China over Tibet). It seems to me that religious people are all supposed to be peaceful. Sure, the Bible and the Koran have violent passages and even urge their reader to enact violence on the "infidels or non believer or wrong believers". Catholics have fought wars with Protestants (I mean real wars with armies lead by Kings and Emporers). The people of Islam have fought wars between different factions such as Shiite vs Suni. Yes, the war between Iraq and Iran that preceded the first Gulf War was sectarian and the final battle was the largest tank battle since WWII. The majority of the casualties in the second Iraq war were due to sectarian violence in the form of car and truck bombs rather than American guns.  The killing by American Christian radicals has been by bombs for the most part. The deliberate assault near Waco, TX that ended up burning men women and children in a Christian separatist sect in their compound was a terrible thing and a black mark on the reputation of Federal agents who "cowboyed" the operation when it could have easily been peacefully ended with the capture of the leader on one of his many trips to town for supplies. Oklahoma city was a revenge killing intended to kill as many federal workers as possible.

How do the architects of such heinous crimes justify their actions to themselves? I believe that it begins with a typical young "believer" who is following in parents foot steps and not really sure what he believes but goes through the motions to be socially acceptable. As time progresses and learning begins, either wisdom or zealotry  begin to take over. The wise believer holds fast to his common sense and humanity while the zealot begins to focus on specific passages that demand action and obedience. The zealot may have too much humanity to go over the edge into radicalism, but if he does not then we have the makings of a pro-active radical extremist. In times past, contact with others of a similar ilk was less likely than it is today with the internet and social media. Once radicalized, a zealot also has a vast library of stimulating oratory to urge him on and  many technical manual to teach him how to act out his fury in a violent way. 

True Believers who are Humanly Wise must rise up to oppose these dangerous men. Neither Islam nor Christianity want their bitter wine. We must speak out against violence and bigotry while we still can.