One reason why so many dispensationalists oppose and warn against any peace agreement between Israel and the Arabs is because they have been teaching that "there can be no peace in the Middle East until Christ returns." Any peace treaty or agreement between Israel and Arabs would tend to discredit their dispensational prophecy speculations, so to protect their credibility, they lobby against all such peace treaties and they ask their followers to lobby their Congressmen against them.
Here is an example of such teaching: "We could admire our politicians who want to bring peace to the Middle East, but my contention this morning is that there will be no peace in the Middle East. There may be a truce, so we’re glad that they can work toward a cessation of hostilities that will last for a while, but ultimately there can be no peace in the Middle East until the triumph of Jesus Christ to the city of Jerusalem and specifically to the Mount of Olives." - Erwin Lutzer, pastor, Moody Memorial Church, Chicago, Illinois, preached on March 3, 2013.
Dispensationalist prophecy buffs commonly teach that 2/3 of all the Jews have to die before Christ can return and bring peace to the Holy Land. Any lasting peace agreement to protect Israel would call that, and all their other bloodthirsty Armageddon Theology scenarios, into question, and would presumably put the Second Coming on an indefinite hold until such time as the peace agreement falls apart, and everybody over there can go back to killing each other.