From Why Israel Feels Threatened, by Benny Morris, NY Times, Dec. 29, 2008:
... The birth rates for Israeli Arabs are among the highest in the world, with 4 or 5 children per family (as opposed to the 2 or 3 children per family among Israeli Jews).
If present trends persist, Arabs could constitute the majority of Israel’s citizens by 2040 or 2050. ...
Friction between Israeli Arabs and Jews is already a cogent political factor. In 2000, at the start of the second intifada, thousands of Arab youngsters, in sympathy with their brethren in the territories, rioted along Israel’s major highways and in Israel’s ethnically mixed cities.
... Down the road, Israel’s Jews fear more violence and terrorism by Israeli Arabs. Most Jews see the Arab minority as a potential fifth column.