The truth is that there is nothing in Judaism that states that a Torah observant Jew shouldn't serve in the army, especially a Jewish army that protects Jews and the Jewish Land and Jewish State, the State of Israel. It's actually a very important mitzvah, Torah commandment to serve and even risk your life.
Not long ago, there was a big controversy in Torah Tidbits about that issue. Phil Chernofsky who has edited/written Torah Tidbits from its inception wrote about the importance of army service. Then Rabbi Leff of Matityahu countered that he was incorrect. And the following week Rabbi Chaim Wasserman, my NCSY rabbi, wrote about how Jewish Law demands army service. The three articles can be seen here. Following are excerpts.
On the other matter of the IDF... I believe, with all my heart, that there should not be exemptions for Torah study. From the Torah we learn that for a MILCHEMET R'SHUT, an optional, non-essential war, there are several exemptions allowed. These include a person who has built a home and has not yet lived in it, a person who planted a vineyard but has not yet had a yield from it, person who has betrothed a woman but has not yet married her... and one who is afraid (different opinions on this, but most interesting is one who is afraid because he does not keep mitzvot properly, to put it mildly)... For a MILCHEMET MITZVA, an obligatory war - and this includes a defensive war in which the survival of the people is at stake - a Chatan joins the fighting even from his Chupa, etc. And the Torah student leaves the Beit Midrash. There is no doubt that we are in a situation of Milchemet Mitzva with enemies within Eretz Yisrael, neighboring Israel, and in other countries within missile range.Rabbi Leff:
...Bottom line, it is the right thing to do for an eligible fellow, to serve in the army in some framework. And it will also be a Kiddush HaShem (or at least, alleviate a possible Chilul HaShem).
It was mentioned there that all deferments for yeshiva students should be canceled and compulsory sheirut leumi be imposed on all girls as in a milchemes mitzvah all go out to battle.Rabbi Wasserman:
It is very presumptuous to negate a principle that countless Gedolei Yisroel (not only from the Charedi world but also others such as Rav Tzvi Yehudah Kook and Rav Avroham Shapira) upheld that Yeshiva students be deferred from army service and girls be exempt from sheirut leumi, by quoting a Chazal that they obviously also knew.
The issue of the tens of thousands of young men who are immersed in Torah study and as a result seek a permanent deferment from army service is arguably one of the primary issues which has divided the Torah-true community these last six decades. The gedolim who have opined that Torah comes first can be listed and named; they are not countless. And then there are, for sure, the dati-leumi gedolim who have concluded quite differently.
Both camps have quoted sources of our chazal and have pointed to different relevant piskei halacha in RaMBaM's Mishneh Torah. Within the limits of these shared lines I would refer your interested readers to yet another passage in RaMBaM's Hilchot Yesodei haTorah 5:10-11 where he clearly establishes that talmidei chachamim will be held responsible for damaging chilul Hashem that can result from their behavior...
...Then we have to recall the immortal words of the NeTZiV in his commentary to Moshe Rabeinu's question to the members of the tribes of Reuven and Gad when they looked to avoid going to war as the nation stood on the banks of the Jordan River: "Your brothers will go to war but you will remain here?!" he asked. This, explains the NeTZIV, would have constituted an "avlah", an unjust wrongful act that would be perpetrated against all of Israel (Ha'amek Davar, Bamidbar 32:6).
In most recent decades, the religious demands/expectations of the dati le'umi, national religious community have increased in terms of levels of observance. In Dati Le'umi circles there are many young men and women in the IDF. Some serve as part of yeshivot hesder in special religious units, others after finishing mechinot special preparatory programs and others go straight into the army after high school. There is much less of a difference between those soldiers and the religious practices of the chareidim. Also, more and more IDF officers are Torah observant, seeing their army service as the greatest mitzvah they could ever do.
The Tal Law, which in recent years determined the conditions of the exemptions is no longer in force and now there are all sorts of political and public arguments about how universal the Israeli army draft should be.
The media and many politicians are pushing for maximum chareidi army service, like Defense Minister Ehud Barak's demand of 90% enlistment. Just like most other of Barak's statements, it may make great headlines, but it's neither realistic nor intelligent. Barak like most/all Leftists conveniently leaves out facts.
One important thing to take into account is that there are many able-bodied Israelis who get deferments for other reasons, or even fake their reasons, because they don't want to serve at all. I was glad to hear Housing Minister MK Ariel Atias bringing up the subject when interviewed on Israeli television. Many Israelis get "sports deferments," rather than time off for special training. In most cases their talents are not Olympic world class sports talents nor more valuable to the Jewish State than many of the yeshiva students are to the Torah world. If yeshiva study exemptions are to be reduced, the same should go for the sportsmen, university academics and others.