I think one cause of Extremism is impatience. Seeing others taking shortcuts while not able to patiently warn or advice them, so an extremist approach is taken. This impatience could be a mixture of jealousy and pride. Once ensnared in this exremist behavior, the pride and jealousy would be there to make sure one stays that way.
Another cause, which is paradoxical to the above, is by failing to react quickly towards certain problems. Now this is the trickiest one, for it requires a very holy soul to respond in a quick and accurate manner, or else, the disaster is usually very disturbing.