Robert A. Pape finds that most suicide bombing is driven by political rather than religious extremism.
Robert A. Pape, "The Strategic Logic of Suicide Terrorism," The American Political Science Review 97, no. 3 (August 2003): 344
First, suicide terrorism is strategic. The vast majority of suicide terrorist attacks are not isolated or random acts by individual fanatics but, rather, occur in clusters as part of a larger campaign by an organized group to achieve a specific political goal. Groups using suicide terrorism consistently announce specific political goals and stop suicide attacks when those goals have been fully or partially achieved.
Second, the strategic logic of suicide terrorism is specifically designed to coerce modern democracies to make significant concessions to national self-determination. In general, suicide terrorist campaigns seek to achieve specific territorial goals, most often the withdrawal of the target state's military forces from what the terrorists see as national homeland.