"Sharon's plan to pull out of Gaza and the northern West Bank next year enjoys wide public support in Israel, but a determined minority of extremists could yet scupper it."
"Israeli Public Security Minister Tzachi Hanegbi warns they may attempt to destroy the Al-Aqsa Mosque, a Muslim shrine on Jerusalem's Temple Mount, perhaps by crashing a bomb-packed aeroplane into it."
"Fear of a war between brothers has deterred previous Israeli governments from removing even the tiniest, most troublesome settlements...Could the Gaza withdrawal be even more traumatic?"
"One-fifth of the soldiers in Israeli combat units are either highly religious or from settler families. Would they obey orders to evict Jews? Other settlers view civil disobedience, and even mutiny, as legitimate means to avoid surrendering land they consider holy."
http://www.economist.com/world/africa/displayStory.cfm?story_id=3092942---
Only a small fraction (the article says 20 to 25,000) of the settlers are extremists, but it only takes a few people to create another big problem for Israel.