First examine the warrior psyche: In all societies a few will wish to elevate themselves to an ultimate warrior status, i.e.: Assassins, Irgun, Nazi S.S., Marines, Gurkha, Hamas, Napoleon's Old Guard, Ninja, Commandos, Spartans, etc. Those who self-image themselves as ultimate warriors obcess over fear and how to innoculate themselves from it. The warrior caste they join requires devotion to its many mantras, some of which are: Devotion to authority, physical and mental perfection, emotional self-control, never be taken prisoner, die for your brothers, make the enemy die with you, etc. Through initiation and group acceptance, the warrior's new belief system has a new fatalism. The warrior now has a part ownership in the caste and the final price of admission is that the caste controls the warriors fate - Ours is not to reason why, ours is but to do and die.
Second: Very few true warriors can be mercenaries, people are always more willing to fight for an idea. The most effective warriors see themselves as leaders ("An Army of One" plays to this)and come to realize that greater leadership requires greater self-sacrifice and that ultimate leadership requires ultimate sacrifice, namely death. Warriors commonly seek hero status from the group they choose to represent either because of a need for superiority or a need to overcome some character inadaquacy (perhaps being bullied when young).
Third: The warrior caste must have a significant cause available and tactically convenient to it. The warrior caste must also see itself improved and elevated by joining any cause. If it does, it will commit its fully initiated true-believers. The death of the member warriors is simply an extension of the operational tactics. Their death is necessary as a recruiting tool and a demonstration of the groups solidarity and devotion.
Fourth: Forensic tests of tissue samples that could found of suicide bombers in Iraq show that many were not sober. High levels of narcatics and stimulants are commonly found, so much for fear.
Fifth: Tribal/hierarchical obedience in muslim societies is very powerful and ingrained. So that is easily transferred to clerics, imams, bin Ladens, Zarqawis, etc.
In summation: There is a combination of individual nurturing and lack of direction, tribal allegiance, historical inertia, munition technology, culture clash, drug intoxication, religious civil war, racial hatred, and political ascendancy, all at work here. It will not end until all facets are addressed.
Also, several sources provide financial rewards for the martyr's family here on earth. In these ways a marginalized dead-end loser becomes a hero in death that he knows he can never be in life.
Until the koran is rewritten or reinterpreted this will not change. There is trouble in River City, most definately.