This very interesting article by Sefi Rachalevsky, called "Dangerous Judaism" discusses the halakhic ruling of "din rodef" and how certain right wing rabbis have applied it to those who would withdraw from Gaza or the West Bank. This is the same halakhic excuse that Yigal Amir used in killing Yitzhak Rabin.

. . .the execution of din rodef is mostly in the province of the individual rather than that of rabbinic rulings. The rulings provide the principle, but the individual is the one who conducts the execution in din rodef, not the court. Din rodef deals with a man chasing after another man and trying to kill him. Anyone who is capable thus has an obligation to intervene, without waiting for a specific ruling that goes beyond the declaration of principle. The pursuer must be stopped with a minimal amount of harm. As the halakha puts it: If the pursuer can be stopped by cutting off his hand, good. But if there is no choice and the only way to stop him is to kill him, then kill him. That is why it was so important for Rabin's assassin to explain that he had considered whether it would be enough to "merely" paralyze Rabin, but reached the conclusion that it would not be enough for the purpose.

Rachalevsky discusses the roots of din rodef as it applies to relations between Jews and Gentiles (rather than, say, to the case of seeing one person about to murder another and stepping to try to stop it).

The problem is that Rabbi Nebenzahl [the rabbi of the Old City, who ruled that "anyone who hands over parts of the Land of Israel to gentiles will be punished according to din rodef"] is correct in saying that the view that din rodef applies to those who give away parts of the Land to non-Jews - or to anyone else who wishes to harm Israel - is well-grounded in the halakhic literature. It is impossible to sweep this viewpoint away with the statement "a Jew doesn't murder another Jew," as people did before the Rabin assassination. Rabbi Nebenzahl's correctness is just the tip of the iceberg, so anyone who tries to bypass him and not deal with the sources will crash into his argument and be shattered.

The root of the matter is the long years of exile and suffering that the Jews underwent at the hands of non-Jews. Those years gave birth to extensive halakhic and kabbalist writings. Central portions of those writings turned the pain into secret vengeance that could not be actualized. Protected by their inability to take practical action for revenge, the great rabbis of Israel let loose with detailed descriptions of the inferiority of the "goyim" (non-Jews), the vengeance they deserve and what would be done both to them and to Jews who collaborate with them after the Messiah's arrival.

Rachalevsky calls for a revision of the halakhah in this matter out of the recognition that Jews are no longer powerless, but dwell in a sovereign country of their own with a powerful army. He says, "The Diaspora is not protecting us anymore. Everything in our time has become practical, programmatic, possible. Those who do not dare to conduct a thorough reform of holy Jewish texts,* out of an understanding of the enormity of the revolution in which the Jews have become masters of military might and sovereignty over their lives, will not survive."

*the original translation was "of the Jewish liturgy," which is not an accurate translation of the Hebrew original -- כתבים היהודיים המקודשים.