Violence of an ideological nature, often including a perceived sense of honor and nobility, service of a greater cause, and possibly personal redemptive aspects has always existed across cultures. Jihadi terrorism is simply the most 'famous' current manifestation of this trend. It is really only 30-40 years old as an ideology, up until the late 70s/80s most Arab revolutionary and terrorist organisations were leftist. Jihadi terrorism is really a syncretism of Islamism, Leninism and Fascism.
If we only look at the present, forgetting it is simply a snapshot of history, rather than a longer term context, perspectives can get a bit distorted.
Norman Cohn - Pursuit of the Millenium (about medieval Christian millenarianism) or William Pfaff - The Bullet's Song: Romantic violence and utopia (about 20th C secular figures) are both fantastic books that might put it into a greater context. It is useful to consider other forms of ideological violence and what they have in common before drawing conclusions on individual manifestations of such violence.
Radical Islam is just that, radical (not conservative). In the West, a traditional religious upbringing is negatively correlated to extremism. Many jihadis are new converts or were 'cultural' Muslims only before.
That's not to say that it is completely 100% unrelated to Islam, the ideology is necessary for ideological violence of course. But the ideology in question here is a modern one rather than traditional.
