I don't understand why the majority of the religious Zionist world opposes land for peace (ideologically). Let's assume for a moment that it's a virtual certainty that withdrawing from parts of the Judea and Shomron would lead to saving more lives than remaining in the territories. In other words the aggregate number of lives would be increased if Israel withdraws from land. Why can't Israel withdraw?
From what I understand the prohibition stems from "lo techanaim," which prohibits, among other things, giving non-Jews a stronghold in the land. Now I see no reason why pekuach nefesh would not trump this negative commandment, as it trumps every other positive or negative commandment save idolatry, murder and sexual promiscuity.
When I was in YU Rav Herschel Schacter used to propose a different ground. The Minchat Chinuch poses a question: why doesn't pekuach nefesh supersede the obligation to go to war? He answers that the nature of war is that lives are put at risk and therefore the obligation to go to war is greater than "v'cahi bahem." Therefore Rav Schacter argued that Israel must fight a war and assume causalities and can only cede land if they feel they won't win the war (in other words if the casualty rate is too high). That question is decided by the experts although regarding the disengagement question he argued that the decision should be made by believing Jews as a substitute for the Sanhedrin.
If I remember correctly, Chardal in the past argued that he'd only allow surrender of territory if the existence of the klal was at stake (like R' Yochanan). But what is the reasoning behind this position?
I think one could fairly argue that most of Israel's wars were in the category of milchemet mitzva. The Rambam lists the wars which fall under the category in Hilchot Melachim (5:1)
ואיזו היא מלחמת מצוה--זו מלחמת שבעה עממים, ומלחמת עמלק, ועזרת ישראל מצר שבא עליהםNowhere is there a mention of fighting a war to keep the land of Israel. In fact the Rambam does not even list the mitzvah of Yishuv Eretz Yisroel in his Sefer Hamitzvot (I know there are arguments to explain the seeming contradiction between his statements in Hilchot Melachim and his omission in the Sefer Hamizvot). The communal mitzvah to capture the land is well-supported by Ramban, but even if we construe that commandment into a support for a milchemet mitzvah, the Ramban himself requires consulting the Urim Vetumim prior to embarking on a milchemet mitzvah (he claims Yehushua was required to ask before capturing Eretz Yisroel). Since today we lack the Urim Vetumim, any war to capture the land would be prohibited.
However, it is clear that defending Israel from its enemies is a milchemet mitzvah that even the Ramban would not require permission from the Urim Vetumim. Rabbi J. David Bleich in the third volume of Contemporary Halachic Problems mentions that the Gemara in Eruvin 45a allows defending border towns in Israel even on Shabbos. He argues that since at the time of the Gemara, Israel had no access to the Urim Vetumim, clearly such a war could be undertaken without consulting it even according to the Ramban.
But even if the present wars fall in that category of milchemet mitzvah, those wars are not fought to defend land, but to save lives. If ceasing the war and ceding land would minimize causalities, wouldn't it be counterproductive to fight the war? The only reason we can fight the war is to save lives, but not fighting the war would save more lives. So how could we fight the war to protect the land?
Basically my question is if the only basis for a milchemet mitzvah is saving lives, and not fighting the war (and ceding land) would save lives, why would it be prohibited to give up land under the war rationale?