This is absolutely wrong for 1 simple reason, Just War Theory contradicts the Torah's view of war.
Rabbi J. David Bleich writes (Contemporary Halakhic Problems, Volume 3, Preemptive War in Jewish Law, p. 277):
Not only does one search in vain for a ruling prohibiting military activity likely to result in the death of civilians, but, to this writer's knowledge, there exists no discussion in classical rabbinic sources that takes cognizance of the likelihood of causing civilian casualties in the course of hostilities legitimately undertaken as posing a halakhic or moral problem.
The Maharal in Vayishlach discussing the action of Shimon and Levi regarding Shechem writes:
It seems to me that there is really no question. [A conflict between individuals or groups is] not comparable to strife between two national groups, like the Israelites and the Canaanites. For this reason, it was permitted for Yaakov’s sons to wage war, comparable to that of any nation waging war on another. Although our Torah commands us (Deuteronomy 20:10) “When you approach a city to wage war against it, you shall call out to it for peace,” this [obligation to first sue for peace] does not apply if the enemy has already acted against us. Where they have acted against us in some manner – as in the incident at had where they opened a breach against them by their vile act – we are permitted to avenge ourselves [through war] against the entire nation even when only a single individual was guilty of the infraction, since that individual is a member of the national group.
We see 1 thing very clearly.
Causing civilian casualties in the course of hostilities legitimately undertaken does not pose a halakhic or moral problem. This is in direct contradiction to Just War Theory.
DovBear then came up with the following inane response:
I'm machmir on this I guess. The Hasidim are machmir on sitting in the sukka when it rain; the yeshivish people are machmir on eating the exact precise amount of marror, and I'm machmir on preserving innocent human life.
This answer simply does not hold water for a number of reasons:
1. This so called "chumra" directly impacts the lives of other people. Are you allowed to put other peoples lives in danger so that you can be machmir? By worrying about civilian casualties you are putting Jewish soldiers lives in danger. Who are you to decide that those civilians blood is redder then our soldiers! Last Wednesday we saw the tragic results of this.
2. A chumra is defined as a kiyum of some shita in halacha. The halacha is like A but since B disagrees we can be machmir to be choshesh for that shita. Just war theory has no basis in Torah and therefore cannot be considered a chumra. What kiyum in halacha is there?
Just War theory is another attempt to replace the ethics and morality of the Torah with the morality of modern Western society.